Solution explorer auto hide not Availabale

 After playing with solution explorer in Visual Studio 2008 I lost AutoHide 
feature on that window. when I right click on Solution explorer I see that 
AutoHide is disabled. 

Answer: Two things you can try: 

1. Window->ResetWindow Layout 

2. Tools->Import and Export Settings... Reset All Settings (Whether you save the current settings or not is your choice).