1. "A:\(filename)
The above filename is invalid"

That could be an invalid filename.

2. You can only put so many files on the ROOT DIRECTORY of a floppy. From memory, about 127 shortnames, less if you use longnames. Since it is a limit, I'll leave you to discover that what the exact numbers are.

3. "an error message that says, "filname.ext.*.* The above filename is invalid". The "*.*" is added by default " in some applications.

Part of the learning of using a PC is to learn what a valid filename it. More and more PC owners can't tell what a valid filename would be.

Best of luck and hopefully one of the 3 items above helps.