I'm just guessing, but it sounds like an address was imported into a wallet as a "watching only" address (imported without the private key).  If that is true, you'll need to remember where you got the address from, and you'll need to find the private key for that address.  Otherwise you'll never be able to spend the bitcoins that were received at that particular address.

If you want something better than a guess, then you'll need to supply more information.  As DeathAndTaxes suggested, the wallet, version, and the EXACT error message would be a good start.