It seems like the source of the problem is the activtiy ‘Reply to Mail’ from the ‘Microsoft office 365’ package version 1.14.1 . Throughout my library three different activties from this package (GetMail, Movemail and Replymail) are used. I removed all of them then added a GetMail and a Movemail activtiy and published sucessfully. I then added a ReplyMail activtiy and published again, but this time the original error that I opened this thread for occured again and I couldn’t publish.