What package and version of PGP are you using ?
Make sure you are copying the entire key block, paste it into a text document and save it as "anythingyouwant".asc and then double clicking it should import it directly into your key-chain. Otherwise use the manual importing method.
If it still comes up as not being a valid key then find the source and double check that they have a working PGP key or ask someone else to confirm if that persons key works.
Remember all of the "-----" on each side of the header and footer of the key block count.