diff --git a/mis_builder/models/mis_report.py b/mis_builder/models/mis_report.py
index fd952e18..0d9e397e 100644
--- a/mis_builder/models/mis_report.py
+++ b/mis_builder/models/mis_report.py
@@ -236,7 +236,6 @@ class KpiMatrix(object):
             if isinstance(val, DataError):
                 val_rendered = val.name
                 val_comment = val.msg
-                val = None
             else:
                 val_rendered = self._style_model.render(
                     self.lang, row.style_props, kpi.type, val)
@@ -401,9 +400,13 @@ class KpiMatrix(object):
                     # TODO use subcol style here
                     row_data['cells'].append({})
                 else:
+                    if cell.val is AccountingNone or \
+                            isinstance(cell.val, DataError):
+                        val = None
+                    else:
+                        val = cell.val
                     col_data = {
-                        'val': (cell.val
-                                if cell.val is not AccountingNone else None),
+                        'val': val,
                         'val_r': cell.val_rendered,
                         'val_c': cell.val_comment,
                         'style': self._style_model.to_css_style(
@@ -967,15 +970,15 @@ class MisReport(models.Model):
                     if isinstance(vals[0], tuple):
                         vals = vals[0]
                         assert len(vals) == col.colspan
-                    elif isinstance(vals[0], NameDataError):
+                    elif isinstance(vals[0], DataError):
                         vals = (vals[0],) * col.colspan
                     else:
                         raise UserError("Probably not your fault... but I'm "
                                         "really curious to know how you "
                                         "managed to raise this error so "
                                         "I can handle one more corner case!")
-                if len(drilldown_args) != len(vals):
-                    drilldown_args = [None] * len(vals)
+                if len(drilldown_args) != col.colspan:
+                    drilldown_args = [None] * col.colspan
                 kpi_matrix.set_values(
                     kpi, col_key, vals, drilldown_args)
 
diff --git a/mis_builder/models/mis_report_style.py b/mis_builder/models/mis_report_style.py
index 51e164c0..7b124922 100644
--- a/mis_builder/models/mis_report_style.py
+++ b/mis_builder/models/mis_report_style.py
@@ -7,6 +7,7 @@ from openerp import api, fields, models, _
 from openerp.exceptions import UserError
 
 from .accounting_none import AccountingNone
+from .data_error import DataError
 
 
 class PropertyDict(dict):
@@ -196,6 +197,8 @@ class MisReportKpiStyle(models.Model):
                            average_value=1, average_base_value=1):
         delta = AccountingNone
         style_r = style_props.copy()
+        if isinstance(value, DataError) or isinstance(base_value, DataError):
+            return AccountingNone, '', style_r
         if value is None:
             value = AccountingNone
         if base_value is None:
diff --git a/mis_builder/report/mis_report_instance_xlsx.py b/mis_builder/report/mis_report_instance_xlsx.py
index 6bdcc689..ae7767ec 100644
--- a/mis_builder/report/mis_report_instance_xlsx.py
+++ b/mis_builder/report/mis_report_instance_xlsx.py
@@ -8,6 +8,7 @@ import logging
 from openerp.report import report_sxw
 
 from ..models.accounting_none import AccountingNone
+from ..models.data_error import DataError
 
 _logger = logging.getLogger(__name__)
 
@@ -115,9 +116,14 @@ class MisBuilderXslx(ReportXlsx):
                 cell_xlsx_style = style_obj.to_xlsx_style(cell.style_props)
                 cell_xlsx_style['align'] = 'right'
                 cell_format = workbook.add_format(cell_xlsx_style)
-                if cell.val is None or cell.val is AccountingNone:
+                if isinstance(cell.val, DataError):
+                    val = cell.val.name
+                    # TODO display cell.val.msg as Excel comment?
+                elif cell.val is None or cell.val is AccountingNone:
                     val = ''
                 else:
+                    _logger.info("*** %s %s %s", cell.row.label,
+                                 cell.subcol.label, cell.val)
                     val = cell.val / float(cell.style_props.get('divider', 1))
                 sheet.write(row_pos, col_pos, val, cell_format)
                 col_width[col_pos] = max(col_width[col_pos],
diff --git a/mis_builder/tests/test_mis_report_instance.py b/mis_builder/tests/test_mis_report_instance.py
index c7b7cc2c..848ed8a9 100644
--- a/mis_builder/tests/test_mis_report_instance.py
+++ b/mis_builder/tests/test_mis_report_instance.py
@@ -73,6 +73,14 @@ class TestMisReportInstance(common.TransactionCase):
                 )),
             ],
         ))
+        # kpi with a simple expression summing other multi-valued kpis
+        self.env['mis.report.kpi'].create(dict(
+            report_id=self.report.id,
+            description='kpi 4',
+            name='k4',
+            multi=False,
+            expression='k1 + k2 + k3',
+        ))
         # kpi with 2 constants
         self.env['mis.report.kpi'].create(dict(
             report_id=self.report.id,
@@ -88,13 +96,20 @@ class TestMisReportInstance(common.TransactionCase):
                 )),
             ],
         ))
-        # kpi with a simple expression summing other multi-valued kpis
+        # kpi with a NameError (x not defined)
         self.env['mis.report.kpi'].create(dict(
             report_id=self.report.id,
-            description='kpi 4',
-            name='k4',
-            multi=False,
-            expression='k1 + k2 + k3',
+            description='kpi 5',
+            name='k5',
+            multi=True,
+            expression_ids=[(0, 0, dict(
+                    name='x',
+                    subkpi_id=self.report.subkpi_ids[0].id,
+                )), (0, 0, dict(
+                    name='1.0',
+                    subkpi_id=self.report.subkpi_ids[1].id,
+                )),
+            ],
         ))
         # create a report instance
         self.report_instance = self.env['mis.report.instance'].create(dict(
@@ -114,6 +129,8 @@ class TestMisReportInstance(common.TransactionCase):
                 )),
             ],
         ))
+        self.report_instance.period_ids[1].comparison_column_ids = \
+            [(4, self.report_instance.period_ids[0].id, None)]
 
     def test_json(self):
         self.report_instance.compute()