The classic fix of simply reinstalling the Citrix client for connection issues seems to be more and essential (not sure what's going on with application stability since they've moved to Reciever but that's a topic for another day)- but the current gotcha is the most recent release of client appears to suffer from a bug where intermittently you receive teh error message:

"This version of Citrix Receiver does not support selected encryption. Please contact your administrator. Error 1046: The Virtual Driver is not loaded" - fortunately Citrix have the answer here: http://support.citrix.com/article/CTX133536 ...request a custom build version of Receiver or dig out an old copy of the client (you did keep an old copy of the most reliable version of the client somewhere, right!?!).