First up, could you try direct send option in BulkEmailer to see if that works for MyToken?
If direct send works then that must be something related to httpcontext is nothing in background schedule which causes mytoken throw exception.
We remember MyToken has solved this problem some time ago, please check you have the latest version of our module and theirs.
If you still have issues after that. Please open a support ticket with us, and provide reference to this post, and host login details. We can then take a look.