An unexpected error occurred (file '', line , function '')

[Nuno_Santos]

After updating to the May 2025 Report Server, the error 'An unexpected error occurred (file '', line , function '')' is occurring in reports that had been deployed for a long time.

It appears that the issue might be related to date Slicers. Ig o delete the date slicer visual and redeploy, the error is gone.

[Nasif_Azam]

Hey @Nuno_Santos ,

The error message:

An unexpected error occurred (file '', line , function '')

after updating to the May 2025 version of Power BI Report Server (PBIRS), particularly triggered by date slicers, appears to be a regression or compatibility issue introduced in the new release.

Root Cause (Based on Behavior)

Since you mentioned: "If I delete the date slicer visual and redeploy, the error is gone."

this strongly points to a breaking change in how date slicers are processed/rendered in the May 2025 version.

This issue has been observed in previous updates as well, where:

• Report visuals created using older versions of Power BI Desktop (especially slicers with relative or hierarchical filtering) break after a server update.

• Sometimes serialized visuals (like date slicers) fail to rehydrate properly due to a schema or engine update.

• Certain slicer configurations might not be supported anymore or require a fresh re-creation from the latest Power BI Desktop for Report Server.

Recommended Workarounds

1. Use the Matching May 2025 Power BI Desktop for PBIRS
   Ensure you’re editing reports with the same version of Power BI Desktop that corresponds to May 2025 PBIRS. Do not use the standard (cloud) Power BI Desktop version.

   Download from Microsoft (check for "Power BI Desktop (Report Server)" – May 2025 version)

   Delete and Recreate the Date Slicer
   As you already noticed, recreating the slicer eliminates the error. To minimize future issues:

   • Use the "Between" mode rather than relative date slicers.

   • Avoid any deprecated or custom slicer visuals.

2. Test with Static Dates or Basic Filters: If date ranges are not mandatory for interaction, consider using dropdown or list slicers temporarily.

3. Review Report Logs: Enable and check PBIRS logs (RSHostingService.log) for more detailed stack traces that might indicate failing visual components.

4. Long-Term Fix: 

   If the issue is confirmed as a bug introduced in the May 2025 PBIRS, Microsoft will likely address it in the August or September 2025 update. Keep an eye on:

   • Microsoft Power BI Report Server Blog

   • Power BI Community Forums

5. Temporary Mitigation: If this issue affects multiple reports:

   • Batch reprocess slicers using a macro/script to regenerate affected visuals (if many reports are involved).

   • Report the bug to Microsoft via their support channel with reproduction steps and logs.

If you found this solution helpful, please consider accepting it and giving it a kudos (Like) it’s greatly appreciated and helps others find the solution more easily.

Best Regards,
Nasif Azam