@Emi @Lizbot So sorry to find this thead two years later and to revive it...
I use 3dCoat for SL all the time.
The issue you were having is still here but it is easily fixed.
The trouble is as was explained in this thread : 3d-Coat is unable to export Collada correctly when there are multiple "faces" (uv-sets in retopo room, surface materials in paint room).
The solution I have always used is this :
-Export collada only from 3d-Coat only for simple objects that have only one surface material
-In other cases always export as .obj which you then import in Blender and export as collada from there.