Today I ran out of disk space on my drive C: which caused Vista to constantly swap memory and turn veeeeeery slowly. I brought up the Disk Cleanup wizard and found out that the System queued Windows Error Reporting occupied more than 2.5+ GB:
So it seems fair to say that the built-in error reporting feature caused an "error". Check your Disk Cleanup wizard regularly to avoid unnecessary usage of valued HDD space by queued error messages sitting there and waiting to be sent to Redmond.