BluStar Agent login issue

[AppUser]

I've come across an issue where BluStar agent was working fine with Solidus 8.3 SP1 and for no apparent reason this no longer works. When you launch BSA it comes up with an error message saying “Unable to connect to server” .The BluStar agent log files gives the following error

03-17-2015 12:06:22.649 [I0]BSA starting
03-17-2015 12:06:22.742 [I0]ConnectToITAService
03-17-2015 12:06:22.930 [E]Exception - Configuration system failed to initialize
at System.Configuration.ClientConfigurationSystem.OnConfigRemoved(Object sender, InternalConfigEventArgs e)
at System

We can login to DM using the same machine

Appreciate any kind of advice guys.

Thanks