I suffered this problem while developing an application for a client. Working on my machine the code/forms etc worked perfectly but when loaded on to the client's system this error occurred at some point within my application.
My workaround for this error was to strip apart the workbook from the forms and code by removing the VBA modules and forms. After doing this my client copied the 'bare' workbook and the modules and forms. Importing the forms and code into the macro-enabled workbook enabled the application to work again.