word crashes when we try to either file save(Ctrl +S) or programmatically save word.save() in the presence of our COM addin

Question

Hi ppl,

We have a COM addin for word called Documentum Application connectors. In some machines we find that word crashes whenever our addin is enabled and when we try a File save (CTRL + S) or programmatically attempt save in our code using the API word.save() we get the following exception in our log

System.NullReferenceException: Object reference not set to an instance of an object  at Microsoft.Office.Interop.Word.DocumentClass.Save().

Can somebody let us know what could be the possible reasons this API as well as normal File save is leading to a crash in word. This happens in few machines.
Please help urgently needed.