Thanks for your quick response!
I have increased the size, but that didn't seem to help. I've also searched like a mad-man for that ShellIconCache file but could not find it (with viewing hidden files of course). Do you know where exactly it should be located? as it's not in my windows directory for example
Edit: I've searched for a tool to clear the Icon Catch, found one, cleared it and it still did not solve the problem