Block @ 99%

Hello,

I have 2 PC, 1 XPPro connected to the www, & 1 XP(not pro, twice are SP1)
connected to the one I use and that pass through a proxy on my pc to access
the net. Everything ran fine, but for three days, when attempting to
download something from the 2d PC, the download begins and blocks at 99%, it
looks like it was downloading but is blocked. I tried with (normal) and
without antivirus, firewall, and so on, nothing changed. The user of 2d PC
isn't an expert, so he doesn't play to tweak it. The proxy I use is analogX
Proxy, but I repeat, until now everything ran fine & the settings haven't
been changed. I noted that it blocks little files as big ones.
Does anybody have an idea of what happens and what I could do to correct the
situation ?
Thanks by advance for any answer, (and sorry for my bad english)