There are hundreds of error messages in DOS. Following are the messages that have occurred most frequently.Access deniedThe file is protected or in use by another application.Bad command or file nameDOS does not understand the command or cannot find the program to run.Data error reading drive XAn area of the disk is unreadable. Press R to retry or A to stop (abort). A utility program may be able to reconstruct the damaged area.Duplicate file nameThe file cannot be renamed because a file with that name already exists. It may also mean that the file is being used by someone on the network, and it must be closed in order to rename it.Exception error 12DOS does not have enough room to handle hardware interrupts.File not foundDOS cannot locate the file.General failure reading drive XAbort, Retry, Fail?Usually means that an unformatted floppy is being used. Press A to Abort, format the floppy and try again. This error will occur if a low-density drive attempts to read a high-density diskette.Incorrect DOS VersionAn earlier or later version of a command is on the hard disk, and it belongs to another DOS version. Commands from one DOS version often do not work in other versions.Internal Stack FailureDOS has gotten completely confused. Turn off the computer and restart.Invalid directoryThe directory name cannot be found.Invalid drive specificationIf this message occurs on a valid drive such as C:, the hard disk may have become corrupted.Invalid file name or file not foundAn invalid character in likely used in a DOS file name. Wild cards may cause errors. For example, the command type *.* would cause this error because only one file can be Typed at one time.Invalid media typeDOS does not recognize the format of the drive being referenced. The disk has been corrupted in some manner and is not readable. This error will also occur if a disk was never formatted properly.Invalid parameterDOS does not understand the switch used on the command line. Be sure to use a forward slash (/) for parameters (switches).Non-system disk or disk errorReplace and press any key when readyUsually means a non-bootable floppy is in drive A. The computer looks for DOS on a floppy before it looks for DOS on the hard disk. If an ordinary floppy is in drive A at startup, it causes this error. Remove the disk and press any key.Not ready reading drive XAbort, Retry, Fail?This meant the drive door was left open or a diskette was not in the floppy drive. Either insert the floppy or close the drive door (turn lever) and press R.To switch to another drive after the "Current drive is no longer valid>" message is displayed, press F and the drive letter (or I for DOS prior to 4.0).Not ready writing device PRNAbort, Retry, Fail?The printer is turned off or unavailable. Press A to cancel, or turn the printer on and press R. Also check the cable connection to the unit.Path not foundAn invalid path name was entered.Stack overflowDOS does not have enough room to handle hardware interrupts. A bad expansion card or one that is not seated properly can cause erratic signals eventually leading to this message.System HaltedMeans the computer could not continue due to a hardware or software problem. It can occur if a memory parity error is detected or if a peripheral board goes awry. A program bug can also cause this as well as a virus. Testing memory, testing for viruses and removing peripheral boards one at a time are ways to isolate the problem.Write protect errorThe floppy disk has been protected and data cannot be recorded. Either unprotect it or use another disk. See file protection.