On investigation it was realized that the issue was occurring for all the workflows which were directed to a particular user. The user has all the required permissions as well.
On further investigation it was found that for some reason the SID link between the active directory and the user info stored in AX was broken. When i tried to click the default company link on the user info i got the below message.
So i deleted the user, imported the user again from active directory and gave the same permissions back. Also established the user link with the employee record. Resumed the workflows and things were back on track.