I have just installed MassMailer Demo on my Enterprise Edition Salesforce instance.
It seemed to Install OK but I get errors when using (in System Admin account)
1. Stay in touch, and test emails, work OK so I know the sendgrid interface works.
2. If I try a One-off email I get Insufficient privilege error for all object types.
3. If I try a MassEmail wizard it works up to step 4 but with Send Now, when I click Submit it stays on the Step 4 page and no email is sent. There is no error message.
4. If I try a MassEmail if I select Schedule in Step 4 and Submit it goes to Step 5 and says it is finished, but no email is sent.
I have probably done something wrong in configuration but I don't know what. I am in the System Administrator account so I should have full permissions for everything.
I have the same issue!