Intermittent loss of SSL connection forcing user to re-login

[mcdermottmb]

I have a WatchGuard Firebox X5500e X Peak e-Series. I have 10 users who use IE to access an offsite, secure web-app which is built on .NET hosted on IIS7. All 10 users are intermittently booted back to the login screen and frequently are unable to login again after repeated attempts then inexplicably are able to. There may be days or weeks between events like this. We have captured traffic with wireshark while these events happen and there were no anomalies. We have run a continuous ping test to the application host and there have been no connection issues detected. No other web services are affected. The vendor reports that there are no problems detected on their end and that no other sites have reported this issue. All users report no connection issues when connecting to the application from off-site so their local configuration has been ruled out. Is there anything on the firewall which could cause such an intermittent problem? If not, any ideas on what could cause this would be appreciated.

Thanks