There is both a log in the application, and the Server log in the PBX that may offer some insight into why this happening.
Do you have other PCs that are running off the same server, over the same network, with no issue? If so, then it may be something (another programme, or a setting), specific to that PC. If nothing else seems to work for you, I would suggest stopping all other background applications (one at a time), especially ones that use a network connection , to see if that makes a difference.