Solid tools question for sketch up 8

[keea1111]

Hi,

I'm trying to figure out why occasionally when I'm using the solid tools, some of my models get snagged on this: One or more of the selected objects is either not a solid or is locked. The non-solid/locked objects will be de-selected before this operation is performed. I know my models aren't locked, so they must be not a solid. Can someone help me figure out how to remedy this? What do I need to do to the model to make it considered 'solid'? much thanks ,

[Jim]

Solid, manifold, water-tight. No holes. No stray lines. No internal geometry.

Here's a plugin to help identify problem areas:
http://forums.sketchucation.com/viewtopic.php?t=30504

And a new one that tries to fix solids:
http://forums.sketchucation.com/viewtopic.php?t=33471