I can neither reproduce this with instant conquer nor with a regular siege - is there anything special you did in/to your game? Were you enlisted at any point? Could you upload your broken savegame?
I have the same problem here. I'd noticed as OXeN said in post #15
that the patch enabled a quest where you were enlisted in your own faction. I'd just taken Suno, taken prisoners, taken loot, and then got stuck on the same "You shouldn't be able to read this" screens as Bankoleva posted.
Floris Gameplay 1.53 (updated from 1.52)
Warband 1.153 (via Steam)
WinXP running with /3Gb switch
I'd started on 1.52 enlisted as a Swadian soldier for Harlus. I was forced out as Harlus got his butt kicked so much he ended up in jail, and the time for me to report back before being classed a deserter ran out. The quest ended and all was working ok. Was kinda funny being skint and shunned. I was able to seige after the desertion, and before the patch.
With the 1.53 patch, a message stated it had fixed the broken quest, and the New quest appeared with me at the same rank I was in Harlus's army (C4 Equdor (sp?)) but now with me in my own army (player faction). At the time I installed 1.53, I was (and still am) a Rhodok vassal.
So yeah your theory about it having something to do with enlisting sounds right (for 2 of the 3 reports so far anyway).
I'll register with one of those file upload sites if you want the savegame (or pm me an email to post it to).
A few other minor problems I've noticed.
1/ I'm still seeing the "Missing mesh" for the Imperial Bow and Rhodok dagger. we_vae_bow_imperial, we_rho_sword_rondel
2/ The village Balanli has no terrain (hills). The land was flat with everyone walking around and the village objects were floating above.
3/ I won a 'reinforced' horse at a tourney. It had ~250 HP.
4/ I can't find the brace/volley commands - though that might just be me being blind.
Thanks to you and the team for the great work you do on this mod.
EDIT: Bugged Savefile