thank you- if you read this post ihave what could be valuable information for you. Thanks to dataflow and ScottA for information there is a bug in Claude Bonet.
For example in the model we deleted all bones and joined the mesh and built just two bones just to see if under the most reduced circumstances we could paint anything. It would not paint this model yet it would paint others with the same hierarchy and attributes.
Dataflow and ScottA suggested to copy the file and paste it in another scene. This worked! with the original model we could not paint. Clearly this is a bug that sometimes happens with Claude Bonet.
We use v.9.6 under OS X although this bug reportedly also effects Windows.