Hi Apurva,
For SAML module version 3.5.0 and newer, the encryption module is required. If you do not have the Encryption module installed you will need to install it from the marketplace. You will also need to set the EncryptionKey constant to a 32 character key. The EncryptionPrefix constant should be set to {AES3}.
It may also be the case that you have some out dated JAR files in your userlib folder. The Encryption module marketplace overview page has some details on what to look for and remove.
Mendix Marketplace - Encryption