Error in TIdEncoderMIME "Uneven size in Encode."...

We have a security program used for encrypting documents and we are using the
IdEncoderMIME and IdDecoderMIME components for encoding and decoding encrypting
keys to Base64.  We just added DES which generate a 56bit/7 character key.  When
we try to encode these keys we get the error "Uneven size in Encode.".
Has anyone else encountered this error?  If so, what can we do to get around it?