Hello.
Regarding this issue, it looks as follows:
a recent update for WIndows XP SP 3 seems to have accidentally added 2 flags into the BITS Service Registry entry which are, simply said, invalid there in that place on XP Clients.
The first key is "DelayedAutoStart". According to MS this is valid from Vista and newer only, so -> remove that from a WIndows XP machine since it is not functioning.
The second key (and mostly our cause of 1290 0x50a error for BITS where it appears)
is the flag "SIDVersionType".
On WIndows XP this is invalid for the BITS service also. -> Remove it.
After that, Reboot Windows XP.
Regards
Bernd