SSRS: field shows correct in query but wrong in report preview

You must delete the filename.rdl.data in the project folder. This is a feature for SSDT. After deleting the rdl.data file, it will create a new one on the next viewing preview with the proper query and it will remove #ERROR.

Another possible way, that will make things easier in the future, is to create an external tool, just like described here:

• Go to Tools > External Tools...

• Add a new tool with the following settings:

  • Title: Clear Report Data Cache
  • Command: "%WinDir%\System32\cmd.exe"
  • Arguments: /C DEL /S /Q "$(SolutionDir)*.rdl.data"
  • Check options:
    • Use Output window
    • Close on exit

Now whenever you want to delete your report data cache, just go to Tools > Clear Report Data Cache.