It's possible you have one version of the VC++ 2005 runtime libraries missing/corrupted on your system. There might be many of them installed at the same time, and this is absolutely normal.
The Stand-Alone Addon Manager uses a slightly different version compared to the one used by the full installer BECAUSE some users have the opposite problem, and the one required by the Full installer is missing/corrupted on their own system, so they must use the one included with Stand-Alone Addon Manager instead.
On a system without any problems to the VC++ 2005 runtime libraries, it shouldn't make any difference, because both should work normally.
If you use the GSX Full installer, and that one is working instead, this confirms you are having this kind of problem: the version of the library required by Stand-Alone is missing/corrupted on your system, so you must always use the Full installer instead, at least until you fix the problem, or reinstall Windows...