Hi @hari - welcome to the community!
Apologies for the delay in responding; I know nothing about Nant and not much about Jenkins so I hoped someone who did would step in.
First of all, you are using quite an old version of the scanner (and one that does not support the new SDK-style MSBuild projects for example). Before trying anything else, upgrade to the latest version of the scanner, which is currently v4.6.2.