The reporting module has had a few problems that have repeatedly appeared in the Novib EVO App-Shell environment and elsewhere.
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To make sure that all report queries and report lookups reference existing data reader logins, edit them in the reporting UI and make sure that the Data Reader Login property is set to an existing value (i.e. any value you can choose through the UI).
Report Queries can be found on the Queries tab of the Datasource Details page. Report Lookups can be found on the Filters Parameters tab of the Datasource Details page, by editing any filter parameter with the Lookup or Multilookup type.
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This can be done in a step-by-step way, starting with the most basic un-parameterized query that can provide data for a datagrid-based report and then adding parameters and specialized layouts layouts one by one.