1. Typically NOC for sale is NOT required (atleast under the Maharashtra Cooperative Societies Act, Rules & Bye-Laws.
2. HOWEVER, the Society becomes bound to issue NOC to the member, on the members demand, without taking into consideration any other criteria, to the exception of its outstanding dues. The Society CANNOT take any objections for any type of encroachment (iron griders or whatever) since all these unauthorised activities have to be taken care of by the local civic body (BMC in Mumbai)
3. Since you are not in a position (due to your sale requirements) it is better to remove the same and continue with your work, WHICH otherwise the Society would harass you for months and your sale would be in difficulty.
Keep Smiling .... Hemant Agarwal