This advice is too late I'm afraid, but in the future ALWAYS ask to have the ESN number of a phone (if it's a CDMA phone) before buying it from a 3rd party. A large percentage of CDMA phones on Ebay and elsewhere have bad ESN's. Usually it's because the person selling it didn't pay their bill and got their service turned off. You can try begging and pleading with Verizon to enable the phone for you, but I doubt they will.
I think it has to do with the sim card..might have to get new sim card to activate with Verizon..prepare for activation fee and cost of sim card..not 100% positve on that.. message the seller and ask before going to far..hate to see you stuck with a brick..
There is no sim card in the Palm Pre Plus for Verizon.