What?
I'm going to assume you imported a singular character sheet, but instead it's selecting portions of it instead of the character tiles? When ever you import any character sheet that holds one character on it (which is 96x128 or 3 tiles wide 4 tiles tall), you must save and import the file with the '$' in the front of the name.
An example: $charactername.png.
If you use an 8 character sheet, which is what VX's RTP standard of characters are, then you don't need to do anything special to it.
Anyway, try what I said above about the '$'. This sounds like your problem and should fix it right away.