First off, my technical knowledge/ability with DOSBox is about nil.
Specifically, I'm attempting to run Commander Keen 4: Secret of the Oracle, but I don't think it's a problem with the game itself.

I'll have been playing for 2-5 minutes, when I'll get the message titled "Assertion Failed!" It then explains the location of the error (C:\Program Files\DOSBox-0.63\DOSBox-0.63.exe) and, apparently, the problem itself. Here's what it says:

---
Assertion Failed!

Location: C:\Program Files\DOSBox-0.63\DOSBox-0.63.exe
File: ../../include/serialport.h
Line: 70

(refers you to Visual C++ Documentation)

Click 'Retry' to debug the program (JIT must be enabled)

Abort Retry Ignore
---

Abort and Ignore close the program. Retry does the same after a few seconds.

Logically, the message is telling me DOSBox has a problem with Line 70; problem is, I have no clue what it is or how to fix it.

Any ideas? Thanks in advance.