A drive can sometimes report "Write Protected" when trying to save files onto it or delete files from it.
This typically means that you have connected an external drive that is formatted with an NTFS partition to a Mac computer. MacOS cannot write to NTFS partitions and so will often indicate the drive is write-protected.
Seagate GoFlex and GoFlex for Mac drives include an NTFS driver that can make the drives intercompatible between Mac and Windows, so that may be a good solution.
See Document ID: 214531 for more information.
For all other drives, please see Document ID: 207851 for instructions on reformatting the drive in MacOS.
Reformatting the drive will ERASE ALL DATA on the drive. Please note that Windows partitions (ie, NTFS partitions) and MacOS partitions are not easily compatible at this time without special software, so using an external drive to transfer data between a Windows computer and a MacOS computer can be difficult and sometimes dangerous to your data.