PST Files in Outlook 2003 not opening

I have a PC in my office that i just upgraded from Office 2002 to 2003. Many pst files were in use prior to the upgrade but now some open OK and some don’t. All of the pst files are saved in the same location. The ones that don’t open give different error messages as to why they won’t open. Does anyone know of any issues with pst files and Outlook 2003 that could be causing this??

Thanks