There was another post last week indicating that WebSphere was squawking about the virtualization.
Apparently the WebSphere server is expecting it's own FQDN in the host header.
You could create a rule to replace the Host: header for each server with the expected value, using [LB::server addr] to cross reference the IP with the expected hostname using a class.
I did some poking around, and found 2 recommended non-iRule approaches to work around this problem.
The least invasive way of working around this limitation without an iRule is in DNS: Simply set the forward (A record) resolution of the virtual server name to the virtual server IP, and the reverse (PTR) resolution for each of the pool member IPs to the virtual server name:
virtual server (in websphere.com zone file):
virtualserver IN A 192.168.1.1
backend subnet (in .. reverse zone file )
1 IN PTR virtualserver.webshpere.com
2 IN PTR virtualserver.webshpere.com
3 IN PTR virtualserver.webshpere.com
The other approach is to actually build ALL the WebSphere servers with the virtual hostname, rather than unique hostnames. The A record for that name would point to the virtual IP, and you can retain the "real" server name as an alias for administration etc.
HTH
/deb