I have a 30 day trial of autocad 2016, which I have been using for 15 days. However when I try to open this copy of autocad today, despite saying on the pop up screent hat I still have 15 days remaining on my trial, it tells me that I do not have a valid license and closes the program. I would like to continue using autocad for the full 30 day trial period. Can anyone suggest a solution to this problem?