ASP.NET2.0 session issues

Our env is as follows:

BigIP F5 load balancing 2x ISA standard 2006 servers with perisistent
connections and using least connections
These then web publish to another F5 with 4x IIS6.0 web farm servers
which host ASP.NET2.0 applications.

Until recently, we have been running asp and Vb.NET code with very
little problem. Since upgrading we have noticed many man errors in our
applications and event viewer with something like this:

Event code: 3005
Event message: An unhandled exception has occurred.
Event time: 06/07/2007 08:51:45
Event time (UTC): 06/07/2007 07:51:45
Event ID: 9659ee7ad5d845dfbd54f08d9df7b513
Event sequence: 115
Event occurrence: 1
Event detail code: 0

Application information:
Application domain: /LM/W3SVC/1109917911/
Root-1-128281738213006250
Trust level: Full
Application Virtual Path: /
Application Path: D:\AppWin32\Websites\name of site\
Machine name: servername

Process information:
Process ID: 3180
Process name: w3wp.exe
Account name: NT AUTHORITY\NETWORK SERVICE

Exception information:
Exception type: Application Exception
Exception message: IP address does not match the session IP
address. Request IP address is ISA1, Session IP address is ISA 2.


We have many other environments, but the only difference is that we
are using round robin connections on them. Could this be to blame?

Our thoughts are looking at the possibilty of user sessions somehow
timing out and then switching to the other ISA server and then we get
a mismatch on the cookie/session