I was tring to migrate to Jabber (Wildfire) plus Miranda and I had exactly the same problem. Transfers originated by Miranda doesn’'t work or send corrupted files even though it receives files from Spark Client. (Miranda 0.4.0.3 / wildfire_2_5_1).
Proxy configurations doesnt seem to be necessary inside a local network. Spark does simple transfers with no special configurations.
I was using ICQ Groupware Server (on winXP) with Miranda client and I was able to do transfers with no problem. But my ICQ server became unstable on XP (server closes) and I could not make it work on Win2k (it installs but server do not even start).
I also tried to download a Jabber DLL from Miranda plugins because I was not sure wich one was newer, the one inside Miranda 0.4.0.3 or the one from plugins download page but made no difference.
I believe that the problem is not in Wildfire because transfers occur thru spark client.
Also had Miranda crashes typing messages to a offline registered user.
I was very excited about moving From ICQ GW to Jabeer but we would prefer to use a multi-protocol client as Miranda can do.
We would appreciate if anybody using same configuration could tell something about it.