Networked media player

Please help!

 

I have searched the forum but cannot find what I am looking for. I have three pcs, one of which records tv programmes and the others are (or should I say were) able to watch them via windows media player. The files are dvr-ms

 

One of the pc's has an update to Norton 19.5.0.145 and whilst I cannot be certain since it has been updated I play the networked files. I can see them but there is a message on media player saying

"Windows Media Player cannot find the specified file. Be sure the path is typed correctly...".

 

The other pc which doesn't have that version works perfectly.

 

Having tried many things to troubleshoot the only way that I can get it to work as before is to disable the norton antivirus. It then plays like it used to.

 

I would point out that mp3 files work, its just these video files. 

 

Any pointers would be appreciated.