See that tiny little dot on line 5 of your code snippet?
txtemail.Text. = "";
Should be this:
txtemail.Text = "";
I'm assuming you're a beginner. Once you gain some experience you'll be able to spot these sort of syntax errors with your eyes shut. ;-)
BTW, Sergey mentioned in his answer that your script is open to SQL injection. You might want to take a good look at that...