Sonicwall issue

I have to sociwall tz 170's at two locations same company running a box to box vpn, it works great and has been for years.Recently customer has employed a piece of softwre that lets them receive quotes via the net.the configuration of the program are basically just a web address to companys website.When the customer logs in to the software from either location (both locations have their on internet provider) the software may run for 10 minutes then say no internet connection.Have loaded software on multiple pc's at each site same problem.Load it on my pc at my office runs great.Have loaded it on remote workstations (outside office)also works great. Talked to software vender several times and they say possible caching problem in router.The sonicwalls are the same in both locations using default configuration other than vpn settings. the sonicwalls seem to be the common demonator at both locations any ideas what i might try, maybe disable caching of some sort in sonicwall.