Deleting unused files

I've used CCleaner for some time ~ Brilliant software. however it suddenly found an unused file problem with an IDC file registry key HKCR\idcfile. and cannot permanently fix the problem. as after "fixing" and deleting next time I run CCleaner the same problem is found. Please can anyone help to cure the "Problem"?

What programs use the extension idc ???

I'm very frustrated ~ Help!!!

G