[DS] Metadata file 'Sandbox.Game.dll' could not be found

I've been running a DS for my friends for quite some time now. Due to issues I won't get into I had to rebuild the server OS today, from scratch, so I don't know if this issue is related to that or the update.

Several components/mods are no longer functioning in my DS. (For example Programmable Blocks are dead.) When I look in the DS log I find "Metadata file ... could not be found" for a number of DLLs, repeated for each mod I have that's not working. Examples:

2016-04-14 19:38:48.786 - Thread: 6 -> error CS0006: Metadata file 'Sandbox.Game.dll' could not be found
2016-04-14 19:38:48.786 - Thread: 6 -> error CS0006: Metadata file 'VRage.dll' could not be found
2016-04-14 19:38:48.786 - Thread: 6 -> error CS0006: Metadata file 'VRage.Library.dll' could not be found
2016-04-14 19:38:48.786 - Thread: 6 -> error CS0006: Metadata file 'VRage.Math.dll' could not be found
2016-04-14 19:38:48.786 - Thread: 6 -> error CS0006: Metadata file 'VRage.Game.dll' could not be found
2016-04-14 19:38:48.786 - Thread: 6 -> error CS0006: Metadata file 'SpaceEngineers.ObjectBuilders.dll' could not be found

• I'm using a full Steam install of Space Engineers.
• The files DO exist in the DedicatedServer64 directory.
• I've had Steam verify the game the local files, even though this is a clean install.
• I've even tried adding that directory to my system path and rebooting.

I'm out of ideas and could really use some assistance trying to figure this out.

Thanks