CompuServe Messages

I am having a problem with shadows dissapearing while rendering a large animation. If I render individual frames each has the correct shadows. But if I render a FLC or a sequence of targas either some shadows dissapear or only render in one frame (usually the last). The camera is not moving. Only some objects are displaced in the sequence. I have checked the lights one by one and they all should cast shadows. Any help will be appreciated. I am using a Pentium 90, R3 and have no other effects or routines goin on. -Arturo