Not all paths in the batch file are surrounded with quotes, and there for fail if the batch files resides in a directory whose path has spaces.

The following lines can be fixed as follows:
copy "%INSTALL_SOURCEDIR%*.dll" "%PER_USER_PLUGINDIR%" /y
copy "%INSTALL_SOURCEDIR%*.pdb" "%PER_USER_PLUGINDIR%" 2> NUL /y

and
pushd "%PER_USER_PLUGINDIR%"
for /r %%i in (*) do "%~dp0\UnblockZoneIdentifier" %%i