A computer is suspected of infection, so the SymDiag diagnostic tool is downloaded and launched. However, SymDiag promptly displays an error message and quits.
The pop-up error message reads:
Failed to create temporary folder.
SymDiag must create temporary files for processing while examining a computer. Some malware will change the permissions necessary to access the user's %TEMP% location in order to prevent the use of diagnostic tools.
Create a new temporary directory (C:\New_Temp or similar) and update the system's %TEMP% environment variable to use this new location instead of the default. Full details can be found in Microsoft's article How To Manage Environment Variables in Windows XP.
SymDiag should then run to completion without error. Be sure to chose the Threat Analysis option.
After SymDiag has identified the malware and that malware has been removed, it may be necessary to restore the correct permissions to the original %TEMP% and update the environment variable once more.