get the pointid of this tag, it sounds like your PI system doesn't know who is the buffered owner of this/these tag/s
look in the pi server log file and search for any error messages related to this pointid, or you can use PI-SMT.

Try this but you do so on your own risk.

We get these errors "buffered point not accepting data" or something like that, this normally happend when we move tags from one OPC Server to another and back due to hardware failures. I normally go onto the PI server open a cmd window, go to your pi root and type the following

PIROOT\adm
piartool -sd \911 -bufreset (911 is the tag pointid, sometimes when you have funny chars in the tagname is can cause some problems)

It can take up to two minutes for the bufreset to update on the client side, so be patient.