Simply Accounting Help

Good Morning,

This is my first on here.....I am looking for some help. We currently are running Accpac and Simply Accounting, simply only for the smaller companies and Accpac for our main company. One of the companies is closing office and we are taking over their books. They use Simply, so i thought perfect. I have tried doing a normal back up on diskette and opening it in the other office, nothing....I have tried emailling the file its only about 4mb so not bad....I have tried everything, nothing works, I keep getting an error message which says the following " This user name does not exist. Check that you have entered the correct user name. Its sooo stupid, i don't understand....I used the BACKUP button, I used the SAVE AS button, select A drive and keep the title as backup...the file is their...it zipped it and all, but no matter what i can't open. Any help??? Suggestions???? Anything at all. Their has got to be a way to transfer files from one computer to another??? Thank you!!!