Cipher strength is below the supported 1024 Bits
Unable to decrypt weak-crypto S/MIME message
Low Cipher strength causes this types of errors
Check the Cipher strength
Check the encoding as we dont support RC2 40 Bit Encryption and RC 4
Make sure the Cipher strength is above 1024 (2048 is recommended)
If the Cipher strength is below 1024 , let say 512 Bits .Change to higher bit encryption .
PGP Desktop , Universal Server 3.2 , Gateway placement , S/MIME