Archiving issues

Hi all, i have QB Pro 2005. I have been in business since 1995 and have never archived so it's running extremely slow. my accountant suggested i archive. So i went into File:Archiveandcondensedata and started archiving. it requried me to back up, so i did, but at the end of the back up it said it had encountered an error and it couldn't continue archiving. it suggested to make sure i had enough space on the C drive, which i do. I have ample space on my C drive. i tried again, and got hte same error. Do you all know what this could be? there's defintiely space. it says that it encountered an error in the data that must be fixed in order to continue archiving. and then it says to check to make sure there is enough space. I don't get it. The back up worked, i checked my hard drive for the back up file and it's there. it seems to do the back up, but then it just kicks me out with that error and i can't continue the archiving process. any ideas? Carla