Bandit:

This is (maybe) not a real solution, but maybe it helps.

You could try to:
1 - select your entire model and export it as OBJ; you will keep the design, but will lose the possibility to edit it.
2 - select your entire model, copy it with CTRL-C, open a new instance of SH3D and paste it with CTRL-V; you can then try and save the model in the newly opened program.

In order to be able to help you better, please, explain what kind of computer system you use, what operating system, which version of SH3D, etc

Hans