Fiddler startup aborting due to suspected another session

When I try starting Fiddler2 on my "windows 7 enterprise" box, I get this error message in a dialog box. What could be wrong ? I've tried uninstalling and reinstalling. I've probably restarted windows several开发者_运维百科 times but even that doesn't seem to make a difference. Do I need to delete any files that might have been created during a previous aborted session ?

TITLE : fiddler startup aborted

message : fiddler appears to be running in this user account. Maybe in a terminal services session ?

This indicates that Fiddler's mutex cannot be created-- no lingering files or settings would cause this. If it repros after a reboot, then there's a problem elsewhere. Version 2.3.4.6 (https://www.fiddler2.com/dl/fiddler2alphasetup.exe) this blocking error is changed to a prompt.