Plugins are not compatible between GMS 2.3 and earlier versions of
GMS2, and between 2.3.1 and 2.3.0 for 64-bit GMS2.  
SEMCCD-GMS2.0-32.dll works with 32-bit GMS 2.0 - 2.2
SEMCCD-GMS2.2-64.dll works with 64-bit GMS 2.1 - 2.2
SEMCCD-GMS2.30-32.dll works with 32-bit GMS 2.30 and higher
SEMCCD-GMS2.30-64.dll works with 64-bit GMS 2.30
SEMCCD-GMS2.31-64.dll works with 64-bit GMS 2.31 and higher
Pick the appropriate one and be sure to rename it to the name without the
version number (e.g., SEMCCD-GMS2-64.dll) BEFORE putting it in the
Plugins folder.  Be sure to put it in the same folder as the existing
plugin and not to leave two copies of the plugin in Plugins.
As of SerialEM 3.4, plugins will detect and warn if there are two copies
loaded.

For SerialEM use, you should upgrade to 3.6 before using any plugins from
here.