FWIW: Bad image errors are often interpreted as malware presence.
I would try uninstalling Skype and see if the error remains.
I'd also do some serious malware scans and check the location of the shfolder.dll and the size. Start/Search...type shfolder.dll as the search string...select advanced search options to include system/hidden files...take a look at the location and size.
This system I'm on reflects two, C:\Windows\System32 and C:\Windows\System32\dllcache are my locations, with each file being 25KB.