Netscreen to Cisco connection

I have setup a Netscreen 5XP to connect to a cisco router for tranaction software my company is using. Some of my user when sending a request with more than 2 tranactions get A run time winsock error. I notice that the users that are working fine are using Safenet VPN soft ware they can tranact 100’s of request I firts thought it was MTU needed to be change but that did not help. when I install the safe net to non working machine they work fine Does any one have any solution I am stuck