I am having precisely the same problem. And one of the reasons I paid a very high price for the 8.5-9.0 upgrade is that FINALLY there would be an attempt to clear up errors and insure that this program is as reliable as it should be. I won't be recommending it to anyone until it is.
Using the latest version of Retrospect Professional with Windows Vista and the new service pack beta, I get the following error messages during every backup of my main drive: Writer "NPS VSS Writer" backup failed, error -1101 (file/directory not found). Component "NPS Database" backup failed, error -1101 (file/directory not found). I have been upable to locate any help files or forum postings that relate to this problem. Anybody have any suggestions? Thank you!