Help: error exporting font

I’m trying to export this font, and this error message appears. Please help.

10%20am

Is it possible you have two circle glyphs sharing the same Unicode value?
In font view, you can search for the Unicode, and change the production name of them with Edit > Info for Selection.

thanks — I’ve just tried what you suggested, now getting a new error code: 59%20pm

You may need to update your feature code. Probably unrelated to the above issue.