Timing is crucial
Windows is again driving me crazy. First is the stupid default usage of OBEX:IrXfer instead of OBEX, including undocumented error codes, and now it's the timing when sending items to the Newton. Well, the Newton IrDA stack has some flaws too, but only with Windows it's so tricky. The issue is receiving items which works now a bit differently than the standard procedure (at least on Windows 2000). The problem is that the Newton listens for an incoming connection, accepts it, waits for some action and disconnects if nothing happens.
Turns out that the way that Windows was designed to work clashes with this. If you initiate reception on the Newton, the IrDA activity icon is shown on the Windows task bar. Only then the option to send an item will be added to the context menu in the Explorer. By the time you have waited for that and activated it, the Newton as already disconnected, thinking the peer fell asleep.
The workaround is to open the wireless file transfer panel on the Windows side before that, navigating to the file to be transferred, initiating the reception on the Newton and then sending the item from Windows... not nice, but it works - besides the fact that there is probably still a protocol error in Nitro that I have to fix.