Summary: As mentioned in the title, I had the building design screen open and had changed a few things (wall material and appearance) and moved on to change the roof of a template house (room for two) when the error appeared.
Frequency: This error message has only appeared once, despite the fact that I have tinkered with the various available template designs several times.
Impact: Aside for the message appearing and my having to attempt the desired changes again, there are no obvious impacts on the game nor on gameplay.
Attachment: The Screenshot taken of the Error message
Version: I’m running Alpha 10.5, release-375 (x64). I have no mods or third party content of any kind installed.
System Info: Windows 7 64bit. AMD Phenom II X6 1100T. 12Gig memory. NVIDIA GeForce GTX 680.