Sometimes, it is useful to back off and do a simple howto.
1] make a simple database
2] make a simple relationship
4] this would mean a field that is a number and takes "01" as an entry
5] this would mean a field that is a number and takes "02" as an entry
6] this would mean a calc field that multiples "field01" times "field02" to give "xx"
This eliminates confusion and corrupt databases as possible sources of confusion.
Are you using an auto-entered calculation? If so, clear the "Do not replace existing value for field (if any)" check box.
Or are you defining a field of type calculuation returning a text type? (If you double-click the field definition in Manage | Database, a specify calculation dialot will appear and the return type will be shown in the lower left corner of the dialog box.)