There are several reason for the above error, most probably either your DLL's or Access Form is corrupt.
IMPORTANT - MAKE SURE YOU SAVE A BACKUP-COPY OF THE DATABASE BEFORE TRYING THESE.
Option-1
Try it on a different computer and see if you get the same error (Make sure you have same version of Access on the other computer too).
Option-2
The cause may also due to a syntax error in the code.
Compile the Code using Debug menu of the VBA window.
Option-3
Open the form, select and copy all the objects using CTRL-A, CTRL-C and then open a new form and paste them using CTRL-V, copy all the code as well, Try new form.
Option-4
Make sure that correct DLL is being referenced under Tools, References menu of the VBA window.
Option-5
Create a new database and import the form.
Then imported the form from the new database into the original database and remove the old form.
Hope these Option help you fix your error
Regards