Playing an Early HRE campaign, and the game hangs/stops responding while Fatmid Caliphate is attacking Constantinople during a Jihad. Playing 6.4 with no submods.

01:13:22.907 [system.rpt] [always] CPU: SSE2
01:13:22.907 [system.rpt] [always] ==== system log start, build date: Feb 25 2008 version development ===
01:13:22.907 [system.io] [always] mounted pack packs/data_0.pack
01:13:22.907 [system.io] [always] mounted pack packs/data_1.pack
01:13:22.907 [system.io] [always] mounted pack packs/data_2.pack
01:13:22.907 [system.io] [always] mounted pack packs/data_3.pack
01:13:22.907 [system.io] [always] mounted pack packs/data_4.pack
01:13:22.907 [system.io] [always] mounted pack packs/localized.pack
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12590, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12591, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12592, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12593, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12594, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12613, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12614, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12615, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <label_unit>, at line 12616, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
label_unit referenced non-existent unit
01:18:53.061 [game.script] [error] Script execution error for <define_unit_group>, at line 12618, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
Error in battle script command 'define_unit_group': invalid unit label 'unit15'.
01:18:53.062 [game.script] [error] Script execution error for <define_unit_group>, at line 12618, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
Error in battle script command 'define_unit_group': invalid unit label 'unit16'.
01:18:53.062 [game.script] [error] Script execution error for <define_unit_group>, at line 12618, in mods/SS6.3/data/world/maps/campaign/imperial_campaign/campaign_script.txt:
Error in battle script command 'define_unit_group': invalid unit label 'unit17'.