3049:key unsuitable for signing

Hi,

Originally I have a key pair with a public key from bank which is signed.

bank needs to renewed public key every x years.

what I did:

1) I removed old public key

2) import new public key

3) sign this new public key

4) tried to pgp encrypt, BUT getting this error "3049:key unsuitable for signing"

please HELP, need to make it work in 2 days.

thanks!!!!!