I'm having this problem too. Running as admin doesn't help. Here's the error log.
Code:
10:55:38.020 [system.rpt] [always] CPU: SSE2
10:55:38.028 [system.rpt] [always] ==== system log start, build date: Aug 3 2007 version bld-medieval2-kingdoms-104 (45562) ===
10:55:38.033 [system.io] [always] mounted pack packs/data_0.pack
10:55:38.034 [system.io] [always] mounted pack packs/data_1.pack
10:55:38.035 [system.io] [always] mounted pack packs/data_2.pack
10:55:38.036 [system.io] [always] mounted pack packs/data_3.pack
10:55:38.037 [system.io] [always] mounted pack packs/data_4.pack
10:55:38.038 [system.io] [always] mounted pack packs/localized.pack
10:55:55.372 [script.err] [error] Script Error in mods/SS6.3/data/world/maps/base/descr_regions.txt, at line 1595, column 14
Unrecognised: 'Hashishim' as a region resource class (or hidden resource)
10:55:55.596 [script.err] [error] Script Error in mods/SS6.3/data/world/maps/campaign/imperial_campaign/descr_strat.txt, at line 4584, column 1
Couldn't find character records name (Eustacheii de_Boulogne) in the names database
10:55:55.596 [script.err] [error] Script Error in mods/SS6.3/data/world/maps/campaign/imperial_campaign/descr_strat.txt, at line 4591, column 14
couldn't find Eustacheii de_Boulogne's character_record
10:55:55.596 [script.err] [error] Script Error in mods/SS6.3/data/world/maps/campaign/imperial_campaign/descr_strat.txt, at line 4593, column 39
could not find next child. Children list must be terminated with an end
I had been playing with 6.3 with few problems. Just upgraded to 6.4