We Have TallyGenicom printers MIP480 that our

We Have TallyGenicom printers MIP480 that our route drivers use to print invoices from their Dolphin handhelds Model 7900 LOP. This week we've started having problems with the printers. We purchased both handhelds/printers in Jan 2009. This week we started having problems with printers randomly just would NOT print. We noticed that the READY green light is on but then every once in a while the READY & WIRELESS lights turn/ flash blue every so many seconds. We do NOT print wireless we have a cradle that the handhelds sit in & they print directly from cable hook up in the office & in the trucks. After several times of disconnecting all the cables & plugging them back in the printer will finally print. My guess is that the printer will search for a connection either wireless or cable if it finds something wireless the printer default switches to wireless then the printer won't print. Is there a way to set up the printer so the default is always cable?? Or what would you suggest as in the last couple of days this has happened to 3 - 4 printers.