Are you usin FileMaker Mac or FileMaker Windows on these parallels machines?
Could it be that the users are losing connections because they connected to the database on Mac, then switched to windows and after several minutes of inactivity with Fileamaker, they were disconnected?
There's a setting in Manage | Security that disconnects users when idle and this setting can be disabled to keep them logged on when inactive.
I'm using filemaker under Mac. They switch to windows all the time (And back offcourse) but losing the connection seems to happen at random. Sometimes when they are working in windows and sometimes when they are working on mac (Checking mail, illustrator etc.).
I know about the setting. It was enabled at first so i disabled it and thought that that was the course, but unfortunatly i'm still losing the connection.
Then I suggest reporting this in Report An Issue as a possible bug. That way, Ts personnel should see your post and they can search their tech support database for any similar reports on this issue. It will also add the issue to their list of bugs should they confirm that this is the case.
Parallels routes ports / resources to windows. I don't think this is a windows issue, but how parallels handles network protocol. When windows is shutdown then these resources are not needed. You can adjust networking settings in the Virtual Machine.
If it was a winodws issue then it would happen when just using a windows machine connecting to the mac server. You may need to talked parallels support.
I guess the best way to rule out windows is to use a stand alone window xp machine and see if you get the same results.