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Saving and Loading ZSCurve Files

I am having trouble loading and saving ZSCurve Files. I have not seen any posts dealing with this issue. When I try to load a ZSCurve file, the files are greyed out, thus inaccessible. And, when I try to save a ZSCurve file, I get this message:

FILE ERROR
Error has been encountered while trying to save a ZSCurve.
Saving has been aborted.

Thank you for any assistance.
D