How to change write permission on flash drive?

Drive Partition and Format

1. Open Disk Utility in your Utilities folder.

2. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.

3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed.

4. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erase tab in the DU main window.

5. Set the format type to Mac OS Extended (Journaled.) Click on the Security button, check the button for Zero Data and click on OK to return to the Erase window.

6. Click on the Erase button. The format process can take up to several hours depending upon the drive size.

Some flash drives have a failure mode in which they are irreversibly write-locked by the internal controller when it detects a write error. If you can't erase the drive in Disk Utility, that's almost certainly what has happened. To be sure, test it with another computer, if possible.

Check to see if there is a read/write slide switch on the flash drive.

If not, then you might be able to get it back to read/write with a format as Kappy suggests.