BleepingComputer.com: Error by a Drive Error Check

Hi, Everybody!

I used to use my HP SimpleSave Portable Hard Drive only to save image backups, but I bought a new external hard drive, so I deleted the backup folder in it and a folder called Princess (my computers name) that must be made by my Nova Backup, both empty (0 bytes) to use it with another computer. But I noticed that even being empty it showed almost 100 gygabytes of used space, so before unplugging it I ran my Smart Defrag on it but the result was “No defragmented files were found”; I ran an error (and bad sector recovery) check and about 10 minutes later a small window opened saying “explorer.exe-Application error The Instruction at 0x00000000 reference memory at 0x00000000. The memory could not be written. Click OK to terminate the program.” (No options), so the check wasn’t finish. Does someone know what that means? Is it broken? Can I unplug it? Do I have to do something to fix it first? If I try to unplug it safely my computer says that it can’t be removed “because some program must be using it…”

Thanks in advance for any help.
vidDa