The first link may take care of the first message. The second download on the page, XP_Fix.EXE.
The reason for it happening and also POSSIBLY the reason for the second message might be on this link here. Please read it and then check your add/remove programs for the possible offender. If it is, follow the directions on this link.
I keep receiving this error message -(C:WINDOWS\system32\autoexec.NT. The system file is not suitable for running MS-DOS and Microsoft Windows applications. Choose "close" to terminate the application.) Then, a minute or so later, I receive a second message (MONITOR:can't find agent "bitware NT agent" class "WCNtAgent.) I've copied the autoexec file from the repair folder and placed it into system 32, but when I restart my computer the autoexec file has gone and the above message returns. (I do not have my original XP CD) Is there another way of fixing this without it. HELP ... Peter