[Gatts]

1.) Did this happen from the first time you started the game (well - not in training maps - as these are "dungeon" - but from first time you fought an army in open space on you PC ) ?

2.) what game version you have?

3.) Did you reinstalled the game for this issue?

4.) Have you tried to start for other character? (if it is just not random one-time issue)

If your answers are:

1.) yes
2.) above 1.6.5 (1.6.5 or 1.7)
3.) Yes
4.) Yes

Try to:

1.) Google "64-bit Vista King's Bounty" [I did, but mostly there were very specific descriptions so your input would be needed, sorry fo not helping you much]

2.) Try to search this forum - I have found some issues with 64-bit Vista, maybe this threads may help you somehow

3.) Contact 1C Company Tech Support (directly by email... )
you could probably prepare directx output file, and your HW description (mobo, prc, graca..)