Multiple drivers due to always enable I/O buffer

Hi FvM,Thanks for your reply! the error information is as the following:

Error: The node "upinter:x4|reg522:x5|x322:g116|vflg" has multiple drivers due to the always-enabled I/O buffer "upinter:x4|reg_datar_16"

when I do synthesising for the individual 'module upinter', there is no such error showing.

when I do synthesising for the top 'module adg522' individually, there is no such error showing either.

but when I added the module upinter into the top module adg522 and then do synthesising, many this kind of errors comes out.

the pin of 'reg_datar_16" is a input port of D in the module upinter. in the other modules, it is a tri-state output.