Issue with DataGroup in iRule

I'd make a few minor modifications and retest:

when HTTP_REQUEST {
     log local0. "URI = [string lower [HTTP::uri]]"
     log local0. "Client IP = [IP::client_addr]"
     if { ( [string tolower [HTTP::uri]] starts_with "/salesentrysystem") and not ( [class match [IP::client_addr] equals SES] ) } {
          pool Pool_SES_LINK
     }
}

Check the logs and make sure the request URI and client IP both match your conditions. On a side note, can I assume you want to allow this pool redirect ONLY if the user requests /salesentrysystem* AND the client IP is IN the data group? If so then I would remove the not operator.