I am new to development of visualforce page so I copied and paste the code from salesforce site but it showing an error when I am trying to create a tab:panel

Error: <apex:page> is required and must be the outermost tag in the markup at line 1 column.

 Everytime I try to save a visualforce page in the setup section I get the following error:Error: <apex:page> is required and must be the outermost tag in the markup at line 1 column 1

I get the error if i edit the page, if i try to rename the file or even if i open it up and just hit save. This is happening on all visualforce pages. Any ideas? My Code: (This is just the standard SFDC Login Visualforce page.