Permission denied for writing access

I have a WD Passport. I have been using it for last 1 year. But suddenly few days back, whenever i try to copy something into it, it says “You do not have permission” whereas I am the administrator for the system. Is there any setting with my system or the HDD that I need to change in order to able to write in the HDD again? Please help with your valuable suggestion.

Right click the drive and select  properties then find the tabs for permissions security etc. It might be there. What OS are you using?