Just to clarify/update I did re-download Strategic 5.01 from the link provided in the Polish compatibility fix post with no luck. I've also dropped in Strategic version 5.0 from earlier that day, and with the Polish DLC enabled the game functions/loads normally. Not quite what UG had in mind though. I'll explore a bit more, probably using how he handled the Eagle Warriors as a template.
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-Update- I've got the 5.01 working with specific lines commented out of Strategic 'Data.xml'
Ln 363 <!--<Row Type="UNIT_POLISH_HUSSAR" Tag="CLASS_IRON"/>-->
Ln 1224 <!--<Row Unit="UNIT_POLISH_HUSSAR" PrereqBuilding="BUILDING_ARMORY"/>-->
Ln 1225 <!--<Row Unit="UNIT_POLISH_HUSSAR" PrereqBuilding="BUILDING_WORKSHOP"/>-->
Additional references (see below) do not require removal, the description reference I can understand why, but the resource assignment puzzles me. Still, it's more data to work from. This is starting to point to another load order issue however by my rough guesstimate. Why DLC would be even allowed to load later in a list is beyond my ken.
<Update>
<Where UnitType="UNIT_POLISH_HUSSAR"/>
<Set StrategicResource="RESOURCE_HORSES"/>
</Update>
&
<Update>
<Where UnitType="UNIT_POLISH_HUSSAR"/>
<Set Description="LOC_UNIT_BMOD_POLISH_HUSSAR_DESCRIPTION"/>
</Update>
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-Last update for the night, then I'm calling it-
It's definitely a load-order problem unique to 'load' rather than 'setup'. I have a fix, but it's ugly.
Process:
(1) Copy Poland_Jadwiga_GameplayData.xml to Strategic Industry Data folder
(make a copy from your DLC folder in base game installation directory)
(2) Modify Strategic Industry.modinfo file to include:
"<File>Data/Poland_Jadwiga_GameplayData.xml</File>"
in both file areas (top call and database section), be sure it's at the
top of both file lists
(3) Include:
<UpdateDatabase id="POLAND_JADWIGA_GAMEPLAY_DATA">
<Items>
<File>Data/Poland_Jadwiga_GameplayData.xml</File>
</Items>
</UpdateDatabase>
above the SREComponent database entry.
This appears to seed the database with enough material for the mod to call from, the rest of the Polish DLC can load at its leisure. I tried to accomplish this first with a simple dependency call, but no dice. I'm sure I've dropped a stitch somewhere, and like I said this fix is
ugly. UG will not be able to include Firaxis material or files as part of the real fix. I'm only hoping that this gave some insight as to the specific cause (on the road to a more 'mod friendly' solution) and offer a temporary fix to those willing to self-service a band-aid. Also not sure if I could have gotten away with just the file call in the items section of the SREComponent database update, but done testing/poking the patient for the evening.