Are you using WEP passphrase or Hex Key? If the former, make sure that the casing on the value is the same in PEP and Router config as passphrase is case-sensitive(IIRC) and leading/trailing spaces for sure cause a mismatch.

ie. "helpMe" passphrase on Pronto is not the same as "helpme" or "help Me" or " helpMe".

If the latter, have you verified that the hex key is correct (case is not specific here as the value is converted to binary for transmission from Pronto).