Cannot import emails into custom modules

I have been customizing SuiteCRM and find it is an exceptionally good fork in most respects, and suits our business very well. One issue I have struggled with for a few days is importing of emails ‘into Sugar’ and relating to a Custom Module. The emails import without any issue to Account and Contact but when I try to import them to a Custom Module I get the error “Import Failed because either the message is already imported or deleted from server”. This is not the case as the email is still on the server and is not imported. Any assistance is appreciated.e no issue relating emails to the Custom Module when I send an email from SuiteCRM - the issue is on importing.

Thank you.