It's not DosBox that's the problem. I remember reading that there's a limit that DOS has on the size of COM files. In fact if DosBox has this issue, it's simply correctly emulating a DOS computer, as it should. However, despite the complete lack of responses from people here (despite asking what that limit is, so I could fix my program, and nobody ever replying and telling me that limit), I managed to after HOURS of searching, finally figure it out what that limit is. The maximum size of a DOS COM file is exactly 65,280 bytes according to a Wikipedia article I finally found that had this info.