NSIS integrity check error when installing!

[Emptiness]

I've started this thread to respond to a request for assistance originally posted in the Bug Thread:

NSIS integrity check error when installing!

Currently happening to all mods I try to install... yes I do have BTS 3.19.

I've tried clearing my cache, updating the NSIS installer thing from Microsoft, (didn't work out "not enough memory" even though I have plenty) downloading it again and again from different sites & mirrors, nothing at all works. Please help.

What mods other than FfH2 have you tried installing? If this is happening with mods hosted from different sites then it is likely that any corruption of the installers is occurring on your end, but if you tell me which mods they are I can download them and try installing them myself (to test whether the installers are working correctly). Please provide links to (or at least the address of) the location from which you are downloading them.

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As for the error itself:

If the installer fails its integrity check you will see a message like this:

Installer integrity check has failed. Common causes include
incomplete download and damaged media. Contact the
installer's author to obtain a new copy.

More information at:
[URL="http://nsis.sourceforge.net/NSIS_Error"]http://nsis.sf.net/NSIS_Error[/URL]

If you encounter this problem, installation will not be able to continue. The NSIS web site (linked above) contains a list of suggested resolutions you can attempt.

From the NSIS web site: (Irrelevant portions of quote removed by me.)

How do I fix the problem?

If the software was obtained from the Internet
1. Clear your browser's cache.
2. Disable any download accelerators or managers and download the installer again.
3. Rename the installer so it is a simple one-word name with no special characters (without removing the .exe suffix)
Example: install.exe
4. Download the installer from another source approved by the software developer or publisher.
It might be corrupted on the server, or the connection to the server is unreliable from your location.
5. Update your anti-virus software (if installed) and download the installer again.
6. Disable your anti-virus software and download the installer again.
7. Download the installer using another computer and copy it to the original computer.
8. If you have the nVidia firewall installed, uninstall the program and download the installer again.
9. Scan for, and remove malware and viruses on your system.
10. Scan the hard drive using scandisk, chkdsk, or any other hard drive repair tool.

Final Options
As a last resort, the installer can be executed even though it's corrupted. To bypass the corruption test, pass /NCRC on the command line. To do so, go to Start->Run, type cmd and hit Enter. A black console window should open. Drag the installer into the window, hit Space and type /NCRC. Hit Enter again and the installer should start. This is not recommended!

You've tried #1 and #4 (that I know of). You should try any of the other suggestions that you have not yet attempted.