There seems to be a bug with the particles system in Blender 2.4x
When the particle emitter is parented to an object that has a location IPO, that object can no longer be moved manually.
I’ve posted a bug report on this, but for now the best work around seems to be:
- Remove the particles (Either remove parenting or switch the effect off)
- Do all your animation
- Reinstate the particles
Cheers.