Repro Steps
The YazLoader class (only used for loading Z39.50 in an addon) has a typo and should be libraryname. Also the YazLoader is not loading the zlib1.dll file despite the log indicating it has. It actually loads libxslt.dll a second time. zlib1.dll is a dependency of libxml2.dll and not a direct dependency of yaz3.dll which has allowed it to not work with bundling the zlib1.dll with addons using this. Currently the LendingAvailabilityAddon for Wisconsin is the only user of this code.

[DllImport("kernel32", CharSet = CharSet.Unicode, SetLastError = true)]
private extern static IntPtr LoadLibrary(string librayName);
....
log.Debug("Loading zlib1.dll");
LoadLibrary(System.IO.Path.Combine(path, "libxslt.dll"));