Create Item Action - File Cannot be opened

Hi,

We have a list with few columns and we have Nintex workflow running on list A. One of the steps is to create a new document in a doc library (B) which is based on a template (docx). We can manually create a document and open the document but when we try using the NW2013 "Create Item" Action, the file gets created but we cannot open the file. When we try to open the file, it throws an error "The file cannot be opened because there are problems with the contents". The file name is generated dynamically.

Any help would be highly appreciated.

Thanks in advance.