This issue occurs only on the oldest versions of IncrediMail that run on Windows XP and below operating systems. In order to solve the problem, close the application and go to C:\Documents and Settings\Your Profile\Local Settings\Application Data\IM\Identities{Long Number}\Message Store. Right click on the Folders.imm file, select Delete option and your personal folders will be restored. Also, I suggest you upgrade the program to the latest version.
