doom2 - my edit won't run on prboom

[lugoteehalt]

Hi.

Have just installed prboom and yadex, both splendid. Tried yadex and
modified MAP01, map 1, from doom2.wad and made a pwad which I
tried to run in prboom. But it said there was no tag
in the header of the wad file - it successfully
found the wad file. Did use the ?xyzw thing on the pwad like yadex
readme says.

You couldn't tell me how to fix this could you? All
yadax tells me is that the next available tag number
is 1.

Thanks any help.