When the error message has one of the seven dwarfs in it – eg. Bashful, Doc, Dopey, Grumpy, Happy, Sleepy, and Sneezy. Then this means it’s a low level Salesforce error. You will need to contact Salesforce support.
Before contacting Salesforce support you can also check if there are any custom workflow/process using the same Task action that is part of the managed package. If so try to create a separate task action for the custom workflow. If error still comes up, contact Salesforce support.