This happens when saving the connection info. It was a known bug and was reported fixed in tightvnc 2.5.2
I found this in TrackerBugs
Whitespace in the "Remote Host" field fails to connect - ID: 3529627
The application fails to connect with the message "Connection parameters (host, port, socket, gates) is empty.
Says fixed in Fixed in TightVNC 2.5.2. Date: 2012-07-05 00:09:44 PDT
Sender: knst-tightvnc
How this is not fixed in the 64 bit version of 2.5.2. I uninstalled and installed the 32 bit version and works with out issue.