Hi Viru,
This is a functionality of Studio to open the sql files, which were opened at the time of closing the studio, when the studio is opened again.
To achieve this, it stores them in your workspace and reads them on opening.
But due to some reason, there is some corrupt file present in the location.
You can either go to the location and check if such a file exists and it contains valid values for studio to open or create the same named file in the location so that your studio opens correctly.
Or as mentioned above create a new workspace but you will have to add all the systems back again in the studio.
Regards,
Anjali.