File Format Not Valid

Bob works with both Excel 2000 and Excel 2003 on two different computers, and often transfers files between the two. Recently, he began encountering two messages indicating some sort of error. The first is "33430000: File Format is not Valid" and it is immediately followed by "55430000: File Format is not Valid." The files do save and do calculate correctly, but the error messages are (of course) bothersome.

The only information that we've been able to track down that may have a bearing on this problem indicates that the errors may not be due to the workbooks, but to a problem with Excel itself. The problem seems to be related to Windows Registry conflicts between the current version of Excel and the version previously installed on the system.

Information from Microsoft indicates that this problem could crop up with some (but not all) workbooks used on the problem system. You can find a fuller description of the problem, along with a way to modify the Registry to try to fix it, at this page in the Knowledge Base:

http://support.microsoft.com/?kbid=327764