To anyone having problems placing blocks, this is usually caused by one of two factors:
1. You are running an outdated version of FtD. The developers recently changed the projectiles used by all of our simple weapons, and the mod had to change to comply with it. A side effect of this is that the mod became incompatible with older versions of the game. You should always be using the latest stable version of the game, especially right now with the huge changes being made in the devtest branch.
2. Another mod is outdated or has a broken installation. If one mod is broken it can mess things up for any others you try to add. We've seen this happen with mods made for an older version of the game, mods that were mistakenly installed in the core game files, and mods that were missing important components due to an error by either the user or the modmaker.

If neither of these is the problem, send me your output_log.txt either by uploading it to a file-sharing service or copying it into pastebin. To find it, right click on From The Depths in Steam and click "Properties," go to the tab called "Local Files" and click "Browse Local Files," which should bring up an Explorer window. Go into the folder called From_The_Depths_Data and the file output_log.txt should be there.