1) Uninstalled SSE, scaned for any leftovers - deleted those, searched the disc C for any "vstep", "extremes", "ship" - deleted all I found, cleaned the bin too.
2) Uninstalled all Visual C++ I had on my pc, scanned for leftovers & deleted those too, cleaned the bin.
3) Restarted the pc.
4) Downloaded that All-in-one Visual C++ package, clicked on install_all.bat, installed all successfully.
5) Restarted the pc again, just to be sure.
4) Installed SSE, still getting the Custom Command.dll error.
Back when my SSE was running fine I had these of Visual C++ on my pc:
Microsoft Visual C++ 2005 Redistributable Microsoft Corporation 8.0.61001
Microsoft Visual C++ 2005 Redistributable Microsoft Corporation 8.0.56336
> Microsoft Visual C++ 2005 Redistributable (x64) Microsoft Corporation 8.0.59192 (newer)
Microsoft Visual C++ 2005 Redistributable (x64) Microsoft Corporation 8.0.61000
> Microsoft Visual C++ 2008 Redistributable - x64 9.0.21022 Microsoft Corporation 9.0.21022 (older)
Microsoft Visual C++ 2008 Redistributable - x64 9.0.30729.6161 Microsoft Corporation 9.0.30729.6161
> Microsoft Visual C++ 2008 Redistributable - x86 9.0.21022 Microsoft Corporation 9.0.21022 (older)
Microsoft Visual C++ 2008 Redistributable - x86 9.0.30729.6161 Microsoft Corporation 9.0.30729.6161
> Microsoft Visual C++ 2010 x64 Redistributable - 10.0.30319 Microsoft Corporation 10.0.30319 (older)
Microsoft Visual C++ 2010 x86 Redistributable - 10.0.40219 Microsoft Corporation 10.0.40219
Microsoft Visual C++ 2012 Redistributable (x64) - 11.0.61030 Microsoft Corporation 11.0.61030.0
Microsoft Visual C++ 2012 Redistributable (x86) - 11.0.61030 Microsoft Corporation 11.0.61030.0
> Microsoft Visual C++ 2013 Redistributable (x64) - 12.0.30501 Microsoft Corporation 12.0.30501.0 (older)
Microsoft Visual C++ 2013 Redistributable (x64) - 12.0.40664 Microsoft Corporation 12.0.40664.0
> Microsoft Visual C++ 2013 Redistributable (x86) - 12.0.30501 Корпорация Майкрософт 12.0.30501.0 (older)
Microsoft Visual C++ 2013 Redistributable (x86) - 12.0.30501 Microsoft Corporation 12.0.30501.0
> Microsoft Visual C++ 2015-2019 Redistributable (x86) - 14.29.30135 Microsoft Corporation 14.29.30135.0 (older)
> Microsoft Visual C++ 2015-2022 Redistributable (x64) - 14.34.31931 Microsoft Corporation 14.34.31931.0 (older)
The ones with > are different than what I have at the moment, mostly those were older versions.