Gmod exit when I finish parent

Hello guys.
Need help: I am building a KV in single player but I want to put it in multiplayer, so I wanted to parent, but when I click the right mouse button, it simply closes. What should I do?

OBS.: Sorry if my English is bad, I am Brazilian. Must practice my English.

I guess you meant crash. What kind of parenting you using? Tho, old versions can crash Gmod very easily.

I use multi-parent. I think everyone uses this tool to parent.