If you have any problems with sfall, your first action should be to ensure that you're using the latest version. If that is already the case, then hopefully your problem is mentioned here.
In ddraw.ini, in the [input] section, change BackgroundKeyboard to 1 and see if that fixes the error. If it doesn't change BackgroundMouse to 1 too.
In ddraw.ini, in the [Graphics] section, change Mode to 4 or 5.
sfall doesn't play nicely with any compatibility mode settings, so it refuses to run with them turned on. Turn them all off. Do this by right clicking fallout2.exe, switching to the compatibility tab and unchecking everything.
In the [Misc] section of ddraw.ini, make sure WorldMapFPSPatch, WorldMapFPS and WorldMapDelay are all set to 0.
sfall requires a specific version of fallout2.exe. (specifically, the american version of v1.02) Don't try using it with anything else; it simply wont work.
In most cases, you can simply swap your exe out with the american one, and everything will work perfectly.
sfall requires windows xp or above. Don't try using it on windows 9x.
This is caused by the proactive defences side of the virus scanner noticing that fallout is displaying suspicious behaviour. Either turn behaviour analysis down/off, or add the fallout folder to its exclusion path. It's not a false positive as such, because sfall does indeed pull some stunts which would look suspicious to a virus scanner.
Not actually an sfall bug, but a problem with the way windows parses dll resources when you're using a multibyte character set. You need to be using a multibyte MUI like Chinese to trigger this one. Viewing a folder containing sfall will lock up windows explorer, and when running fallout it will be unable to load sfall's ddraw.dll causing it to assume direct x isn't installed properly. It seems to occur somewhat randomly, so there doesn't appear to be much I can do inside sfall to work around it.
This can be caused by the windows explorer hang problem, so check if that applies to you.
If you're using graphics mode 4 or 5, then make sure your DirectX 9 installation is up to date. If you're on vista/win 7 and have DirectX 10/11 then it doesn't automatically mean that you have the latest version of DirectX9, so install it. Specifically, when using mode 4 or 5 sfall requires D3DX9_30.dll.
If you're on vista, or windows 7 and have UAC enabled, then do _not_ install fallout 2 to the program files directory. Instead pick a path like 'C:\Games\Fallout2'. The same thing applies to any game that you wish to mod. The program files directory is protected by windows, and you'll find yourself either unable to modify the files in it, or your files will end up getting mixed with copies in the virtualstore.
You've just installed sfall on top of another mod which already included it, and which had custom settings in its ddraw.ini file. You've just overwritten all of those custom settings with sfall's defaults. Compare the new ddraw.ini file to the one that came with the mod, and remake any changes. This particular error is due to the 'CitiesLimitFix' line, but make sure you get all the changes, because others may cause more subtle problems later on rather than an obvious crash at startup.
There is no longer an official build for windows 9x. This is nothing to do with the move to sourceforge, but rather due to the switch from visual studio 2005 to 2008. (And later, to 2010) Building win9x compatible binaries is not supported with vs2008. It's worth noting that vs2005 didn't support win9x either, and a large amount of messy hacks (see win9x.cpp in svn) were required to get it to build. The resulting version lacked some of the features of full sfall, and since 1.46 had ceased working completely. Building a win9x version by now requires fairly substantial code changes as well as switching to a far older compiler, but is probably still possible.
Applications compiled with vs2010 do not support windows 2000, or versions of windows xp prior to service pack 2. There is an untested and unsupported version of sfall built using vs2008 available from sourceforge for any remaining win2k users.
There has never been a fallout 1 version of sfall. The mod that was available that shared the same name was not sfall in the fallout 2 sense, but mostly just a glorified fix for the black screen issues. This can now be accomplished more easily, and with less restrictions on which version of the fallout exe you need to use, with the resolution patch.
I don't intend to make anything along the lines of sfall for fallout 1 myself.
There is an active thread on sfall development at NMA. Post your problem there, and assuming your question isn't too obvious/already answered, then hopefully someone will answer.