The attachment in this module had a size attribute. Mendix introduced 7.5 on the filedocument level.
In which java-action you get the error?
EDIT1:
change
attach.setSize(bodyPart.getSize());
into
attach.setAttachmentSize(bodyPart.getSize());
BTW The Email POP3 is not compatible with 7.5.1.
i'm comming from 7.1.0
I get the error in EmailHandler