Using Application.Inputbox.........getting type mismatch error

Hi, i have the following code.........

err_msg_1 = Application.InputBox("The input file checking procedure has detected what could possibly be an error with input file.  A required Header string was not found.  Do you wish to ignore this and continue with running the program or do you wish to end the program now?  (C)ontinue or (E)nd")

However, when i run it i get a type mismatch error at this statement........any ideas?

err_msg_1 is defined as type string.