Saving Assembly Error

[Anonymous]

I've just created my frist semi-complete assembly.  But, I'm now having trouble saving the file.  I get the following error:

"The current Design View Representation is locked. Changes against it will not be saved.  If you want to keep those changes please create a new Design View Representation or unlock the current one."

I have never locked the assembly so I'm not sure why it is locked.  I do not want to try and save as a new design view for the fear of losing what I have - not sure how to do it.  If someone could help me save it as a new design view representation or teach me how to unlock it that would be great.

I would like to learn how to do both though.

Thanks!