Just a report, after updating browser to 21.0.1200.0 everything was ok!
Added just a textbox to a project. Preview looked ok, but when i changed tabs, or minimized window error occured:
<img src="https://dl.dropbox.com/u/62601881/error/error.jpg" border="0">
After browser update, everything worked fine.
On Chrome 21.0.1180.89 m and IE9 9.0.8112 everything was ok.
System spec: Win7, 64bit, AMD Radeon HD 6700.