I am a recent convert to jME, I noticed on the tasks (before the forums were trashed) that you were looking to develop a Blender importer.
To get to the point, I have created exporters for other engines, and decided to work on a Blender exporter for jME, exporting to jME XML (for several good reasons, most off all the XML route is the easiest to take).
Unfortunately their are problems with the XML to Binary converter, it creates an invalid binary file, for some tags.
The problem is with the attributes, one affected tag (there are others) is <texture>. The wrap and texnum attributes in <texture> results in a binary file, which when loaded, results in a class cast exception.
I delved into the code and have identified the problem :
In XMLparser.XMLtoBinary.processWrite() any attributes that are not detected, are written out as jME strings, by default. This results in some numeric attributes being written out incorrectly, as jME strings.
For example in <textures> the wrap and texnum attributes are written out a strings, when the jME binary loader subsequently loads these values, it attempts casts them to Integer, which results in the the class cast exception.
I have verified this by adding in the code to detect texnum and wrap and writing these out in the correct type (jME integer), which results in a valid binary file (loads without any problems).
Unfortunately I am in a position where my exporter, as it exists so far, will only work with my corrected version of jME !
I'm happy to provide patches to correct the problems, but am unsure how to go about it, or if I should (do not want to interfere with any work in progress).