There is a patch available for busybox to increase it's zip compatibility. Unfortunately it hasn't been included in the main builds yet.
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Yeah, I saw your upload in the other thread. I still do not know how to use it. Do I use it to replace one of the source files and recompile? Of course, I moved all my source files to the external hard drive to save space, so it may be a while before I get the chance to recompile again, so I'll just use DSCompress for now.
In response to the GBA slot RAM comment, it would have no positive effect. RAM in the GBA slot is so slow I have problems describing it using the English language.