This is pasted from a thread in which someone was having trouble building maps in Swat 3 when using Windows 8. All of the following suggestions probable apply to Windows 10 also.
Here was my suggestion for his fix:
* Uninstall Swat 3 but backup any downloaded weapon mods or skin mods and backup any custom missions you have downloaded. You will copy them back into Swat 3 after you have done all the next steps.
* Re-install Swat 3 into a custom folder. The newest installer from GOG.com installs to "C:\GOG Games\Swat 3\"
* Installing Swat 3 to "Program Files (x86)" possibly creates a lot of problems with Windows 7/8/10 machines because it tries to store settings files in "%LocalAppData%\VirtualStore" instead of Swat 3's folder. This might screw up Worldcraft in particular. I would eliminate this as a source of trouble and install to the GOG recommended folder mentioned in the last step.
* The latest GOG.com installer places Swat3.exe into Windows XP SP2 compatibility mode. XP SP3 seems to also work nicely.
* Copy the SAMPLE folder from the TOOLS folder into your MISSIONS folder. Swat 3 does not like building maps in the TOOLS folder. They have to be in the MISSIONS folder.
* Make sure you reconfigure Worldcraft to point everything to the new locations of Swat 3 and the SAMPLE folder.