I've been experiencing this problem for quite some time but I didn't really want to report it because I don't have any adequate explanation for it and I find it somewhat inappropriate to burden and bother developers with yet more random, cryptic reports that hint to absolutely nothing, specially when nobody else appears to be experiencing the same thing (or so it seems from reading what's been posted over here)
It turns out that gpg-agent.exe ceases to function if you leave it unused for a while. How long? not sure exactly, but it doesn't have to be like days or anything. Last time it happened within an hour and a half I believe. Whenever gpg.exe calls for it to be executed (assuming it's not already running, of course, though I have occasionally been left with multiple gpg-agent's lingering in the background when something goes wrong) , it will work right away no sweat. But once it's been used and left to idle, it cannot be "brought back to life" or so to speak; trying to sign, encrypt, edit a key or whatever it is that needs to be done, gpg-agent.exe won't respond and all I get is the copyright message upon executing gpg.exe. During this time, gpg-agent.exe will not use any CPU at all and memory consumption remains perfectly stable at about 4MB.
One time I was actually able to "resurrect it" by enabling a specific combination of debug options along with the usual encryption/signing commands, but I could no reproduce that behavior ever again, so all I can do in order to use gpg in a more or less conventional fashion (which works fine save for the password issue which has to be retyped every time), is to manually terminate the agent so that gpg will start everything from scratch.
This may not sound like a big deal, but it's become yet another layer of complexity in the context of the automatization of certain tasks.
Tested on 32-bit WinXP SP3 with 2.2.0.
Thanks for your time and sorry for the inconveniences.