Error getting License. License Server Communication Problem: E_ADEPT_REQUEST_EXPIRED

This is the message I keep getting when trying to open 3 acsm books my friend has sent me. She sent me 4 and 1 opens, but the other 3 won't, and I've re-downloaded them at least 3 times with the heading always popping up. Please help (and make it simple, please. I get very confused with too much detail).