Ouch... Digital products won't do whole download; all limits set correctly in wordpress; downlo

Hello,

I need some assistance in troubleshooting this within Marketpress - I
have spent several days making sure all the relevant settings are
correct both in my wordpress and in my server to support this, and now
that this is surely not the problem, I think the issue lies within
Marketpress's settings (but, of course, I could be wrong).

The site I am working on (eyevocab.com) is meant to sell digital
products (software), which is why I bought the MP plug-in. However,
the downloads we need to offer post-purchase are at 41KB and larger,
so I've had to do extensive changes within WordPress settings inside
multiple config files in order to up the limits on upload_max's,
memory limits, and execution times (the former is now set to large
memory amounts like 1024M/1G; the latter are all set to no-limit
integer settings, as much as is allowed). However, here is what is
still happening:

Our current product, which we're using to test the system, is 41KB in
a zip file. I worked through all the errors I was getting within
WordPress while this was too big for the small default limits; now, my
process goes fine until after the purchase, when the buyer is sent
back from PayPal to the Marketpress-based shopping cart/store in order
to confirm purchase and get the link to the downloadable product. At
this point, the buyer clicks "download," and the file begins to
download (no error from wordpress, no error shown at all) - however,
the download basically is done within a half-second (too short of a
time to know how much), and the zip file shows up on the buyer's
computer as-if the download has completed normally (but much too
quickly). Then, the file that is actually there from the download is
only 4KB in size, obviously a small fraction of the real thing, so it
can't open at all.

We took our store down in the interim while I'm troubleshooting this;
I really need to get it back up asap. Seriously asap...

So - are there settings/etc for/behind marketpress, which are
pertinent to me having this problem? I do wish there were specific
settings within the plug-in settings in wordpress, which would allow
me to tweak things that are important to selling digital products,
especially large software packages which should be handled well
according to your descriptions of the plug-in you sell. If I can't get
some guidance on these issues, I may need to try and get a refund and
then seek out a more suitable plug-in for my digital products
e-commerce needs. (Which I say only respectfully and out of a need for
help)

Thanks for any and all help you can provide - I've had one hell of a
work-week with this.
Drake Logan
eyeVocab R & D