The first thing to try is on this computer go to Timeslips administrator > Diagnose this computer. You may see a red x under firewall. Click to open port 3050. For some reason I find I often have to click twice. Once it is all green. Close and try Timeslips again. 

Actually, the port needs only be open on the server and not on workstations.

My experience has been that more than likely, that particular machine is not able to correctly resolve the IP address of the server through DNS.  Best bets to diagnose are to (A) Using TSAdmin on the workstations - located in C:\Program Files (x86)\Timeslips by default - verify that you are pointed to the same CFG on the server as everyone else.  It will be at the top next to Installation Path (B) turn off the anti-virus/firewall locally temporarily and see if that resolves it (C) ping the server by name and by IP Address and see if you get delays and/or bad responses.  

Resolve any of the above and you should be good to go.

Thank you for the response. I run the TS Admin and I get this error when I check the condition of the database. 

I also have just started getting the following error when I log into the server, timing is interesting and I bet the firebird database is also in c:/programs

Up until now I've only selected ignore. 

Correction: I know the firebird database is not in C:/Programs I meant the firebird sql instance or something to do with this part of firebird. To clarify I didn't mean the TimeSlips database is in C;/Programs

Using the timeslips diagnostics I found that the firebird service was not started. I clicked on it and it fixed the problem.

If this recurs, it would be a good idea to have an IT professional track down whatever program or issue is stopping that service from running.  That is not normal behavior for it to be stopped for any reason except manually.

If 3rd party malware software is stopping unknown (to it, anyway) services, it should be told to disregard Firebird as it needs to be running for Timeslips to function.