As suggested check to that the Program File is deleted.
In msconfig>Startup tab uncheck everything besides AV and gadgets/stickies. Then in msconfig>Services, hide all MS services and see what is still running.
Startup Programs - Change - Windows 7 Forums
Set a Restore Point, do a search in regedit for irfanview and progids then delete each key containing it. You can do this search with regedit, or RegSearch suggested by SIW2 which is better.
The reason CCleaner keeps finding the key is because it is and empty key from a deleted program, but it is repopulating itself so it needs to be tracked down and deleted.