KRC session to Windows XP (SP3) or Server 2003 (SP2) agent disconnects immediately after connection (viewer reports "connecting lost")
The problem has been documented
Microsoft ended support for Windows XP in April 2014 and for Server 2003 in July 2015. It is recommended to update production systems to later version.
At the time of writing (October 2015), Windows XP and Server 2003 are still supported operating systems for the Kaseya agent, but remote control functionality is supported only in "legacy" Remote Control module: -
1) go to Remote Control > Control Machine page
2) click on hyper-linked agent name to initiate remote session
Kaseya VSA (v7.0 and later)