Sometimes when you import a GEDCOM there are roles that are not standard. These get added to your data base and even if you delete the data you imported, these remain.
If you go to "Build - Template - Source" these extra templates will normally be at the top of the file. If you click on delete for each one, the program will let you know how many times it is used in the "CURRENT PROJECT". If you only have one project, or if you check the item in every project and it says that it is not used in each project, you can delete the source template.
If the source is used, perhaps you can identify where and change it to a standard source or change the source which has an error to a standard format.
This should take care of the error messages you are experiencing.