RDP Connection constant disconnections

Greetings, 

We have 4 PC's  (3 wired, 1 wireless) on the office network that connect to a hosted ASP platform called Right Networks that hosts our Quickbooks files.  We connect by opening an RDP file that opens a remote connection to their server, then we login to quickbooks.  Over the past few months, the connections have been dropping several times a day, sometimes they'll reconnect immediately, other times it will take a few minutes, other times it will time out completely.  Its random when the drops happen, but when 1 user gets kicked off, they all seem to get kicked off, if only momentarily.  I've run ping tests, wireshark scans, but can not find the root cause of these issues.  The comcast modem is the Cisco business unit with wi-fi.  We've tried running new PC's with no firewall/AV, just to see if that could be the issue, but still the same effect.  Let me know if anyone has experience with this and possible resolutions.

Thanks

Millennium