PROF,
there may be an issue with the function valve or cylinder or maybe an obstruction keeping the telescope function from moving in or out.
You mentioned the 'distress' light lighting up? (that's what they call the triangle with exclamation point). Is it blinking when you select the function? How many times? It should blink a certain number of times and the pause and repeat.
In either case using a JLG handset would tell you exactly what is going on so you may have to call a JLG service tech out to check it out.
The service literature wants to check pressures etc on that function to make sure it is correct also, incorrect pressures can cause it to fault out. It could be something like a bad pressure relief valve or a bad pump too.