Online custom form in customer center

I thought this would be a no-brainer but has completely frustrated me.

I want to use a custom record online form to capture feedback but I want to embed it in the customer center so when a customer clicks on the category or the item (info item) it will display like any other page with the appropriate borders and tabs, etc.

I can't do it! No matter which way I do it, I can display the form but when I submit it I continually get the cryptic "An unexpected error has occurred. Please go back and try again."

Since the error gives me no indication of what has gone wrong, I have no idea where to go next. Was hoping to avoid needing to go through a lengthy support call to likely get no help, that someone here has tried similar with success and could tell me what they did to get it working.