If you see an error dialog box with a message like this "Invalid Component id '134'. Cannot Find Component HTML" this is mainly due to pasting invalid HTML code on your page. Please read this tutorial for ideas on how to address this: My site won't load in the Sitebuilder.
You may also find useful:
Solving problems with site loading in Sitebuilder
Why code is not displaying in Sitebuilder or in preview mode
I need a different layout than pre-set ones offered in the Sitebuilder