When HD light maps are enabled and the player has a long view distances or moves through terrain with different lighting scenarios this message eventually occurs. The short-term workaround is to use F3+A to reload chunks.

This will be fixed in three stages:

1. Additional lightmap space as a configuration option
2. Better use of existing space by using rotations/inversions of lightmaps
3. Automatic recycling of lightmaps no longer in the view frustum

Suspended for now - will likely implement a different system soonish