how to enable or disable button when status is "Done" in grid table

[Vishwanath_Pal]

i have created grid table and there is one status drop down list for "Open" and "Done". I have succesfully created a button to convert that grid data into issue type "Task". Now what i want here ...whenever status is "Done" in grid table i want that button(which is created by me) to be disable and when status is "Open" button should be enable...(like if status is "Done" button would be disable so no one can create "Task") any suggestion or link would be great help...thanks in advance