Outside help 2

[CarnivorousJelly]

Hm... check for map cache files under C:\Users\[YOUR USERNAME HERE]\AppData\Local\VirtualStore\Program Files (x86)\Amnesia - The Dark Descent\redist\custom_stories\[YOUR CUSTOM STORY FOLDER]\maps
You have to type the directory name manually because it doesn't actually show up - but once you're in VirtualStore, you can click on the rest of the folders manually. They'll be wherever you saved your maps.
Delete any files* there (there shouldn't be any).
*If you've been saving directly to the program file for your maps DO NOT delete the maps. Move to your desktop, then move them from your desktop to your CS folder (not under Virtual Store).

If that's not it, it might be where you placed the rain particle - it's pretty large, so you should be able to just place it at 0, 0, 0 (XYZ) and have it cover your map.

If that still doesn't work, try this function:
PreloadParticleSystem(string& asPSFile);
replace string& asPSFile with the particle system name (include the .ps extension) in quotations. Should go under OnEnter for your script file

Wow, that's a lot more problem-solving than I normally do :p