Error 400 Show Modal Form

I'm getting an "Error 400 - Form already displayed; can't show modally" error from a UserForm project I've been making. It's attached below. How it *should* work:Use the button "ENTER NEW DATA" to open the UserForm. Submitting the Form should insert the data into a new row below the already filled ones. (the range of Form data starts at row 7)Click on a Non-Empty, Protected cell of Form data, and the UserForm should open, containing the data of that row within its corresponding fields. Submitting the Form should modify only that very row from which it was sourced.When you close the workbook (OzgridMST1.xls), the Form data should be copied into another workbook (on Sheet1) on the same level as OzgridMST1. (I couldn't include it in the . ZIP file since it would have been too massive... Just create a new workbook called FormDBTrial1.xls on the same level.)

Problem(s):When i fill-in and Submit the UserForm for a second time (by either the button or a Non-empty cell), the Error 400 appears and traces back to [UserForm].Show in the Sheet code. I've double-checked my code and can't see what the problem is.When i Submit the Form through the Non-empty cell, it submits into a NEW row, and not the same one! My code used to work, I've tested it many many times. I've triple-checked my code, can't figure.Finally, when I close the Workbook, an Error comes up saying it can't find FormDBTrial.xls, even when it plainly does exist on the same level, same folder, etc.
Everything worked fine until I added the "Copy To Another Workbook" functionality. Been over it and the forum so many times my head is spinning...