You are running a Serendipity version of 1.0.1? And the 1.94 version of the Usergallery gave you an error telling you it was incompatible? Yes, it did.

And once you fixed the version comparison it no longer complained about the compatiability, but then it didn't display the "next page" navigation ...

Running Serendipity v1.0.1, I've recently updated the user gallery plugin to v1.94. Although it warned me about incompatibility issues, I found out it's not to be compatible with v1.1, but should work correctly with v1.0.1, so to get it working I changed the version comparison.

Now all is working ...