I had this same problem after upgrading shozam about 6 months ago. What I found was a corrupted .xml file. Once I copied my backup file into the folder I could modify the existing gallery. I can't say for sure that's what your problem is but worth a try. Save the xml file you have now though. Another solution I found was to download my gallery from my webhost although there were a few changes I did have to make. Then I resaved that one in the same place.Hope this helps.
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