We have had this issue occur in the past.
First, are all of your SimPad -LinkBoxes paired? If not, you may want to pair your sets, how to info. is provided on the laerdal website under SimPads->Downloads.
Do the linkboxes connect to a patient monitor? We found that anytime the students put pressure on the cable from the LinkBox to patient monitor our SimPad-LinkBox set would disconnect from each other.
Are you running off battery or AC power? When the battery comes close to but not completely depleted on the linkbox I've had the simpad linkbox unpair. If you're running on battery, try staying plugged in and see if it makes a difference?
You may want to try changing the RF channels the linkbox SimPad use to connect, too much trafficon the same channel can cause a loss of connection - we have also had this happen before :)
Hope some of the info. above is helpful, if not call your local Laerdal Field Service Tech./Tech. support, have always found them to be super helpful!
RN, Simulation Specialist
Centre for Simulation-Based Learning
Health Sciences Centre, 1M- 5
1280 Main Street West
Hamilton, ON L8S 4K1
Tel: 905-525-9140 Ext. 22063