This has been reported as a bug. But you can try this work around and see if it works. Install Gparted if you don't have it installed. If its not, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:
sudo apt-get install gparted
Once installed, open the application, and before formatting, make sure that you choose the right drive, and Unmount the disk by right clicking on the partition, and choose Unmount, then you can use the format To option, to format it to whatever type of file system you wish. Once done click on the green check mark to apply the changes.