If you (suddenly) get an error like the following (which may vary depending on OS) when generating custom reports, it is likely caused by a recent security update for MS Office.

Good news is that Microsoft realized this problem and provided a “fix it” tool at http://support.microsoft.com/kb/2703186.

This is what happens based on my investigation if you care:

There is an EXD file created for some VB 6.0 runtime files when you use the controls provided by the runtime files in the Visual Basic designer. Those files are located in %APPDATA%\Microsoft\Forms\ folder (which may vary depending on OS). The problem is that, when security update installs new versions of certain runtime files, the EXD files become invalid and hence this error occurs.

To fix the error, you need to delete the EXD files and they will be re-created as needed. To delete those files, you can either use Microsoft provided “fix it” tool from the link above, or go to the folder directly and delete them.

This link http://technet.microsoft.com/en-us/security/bulletin/ms12-027 gives you some details why the security update is necessary and which software are affected.