Prepare a Form issues

I am trying to upate a fillable PDF that I created previously. This PDF has normal text fields and fillable text fields as well. When I attempt to make changes to the fillable fields (deleting, changing where the fileds are so that when you tab it goes to the correct fillable field when being filled out, etc.) and then save the changes, it will not save. I get the following message : "The document could not be saved. Cannot save to this filename. Please save the document with a different name or in a different folder". When I make changes in Edit vs Prepare a Form, the changes save no problem. I tried updating Acrobat but still no luck