Would you please verify that you have a valid DOCTYPE as the first line of your HTML file?

If you’re not currently setting a doctype, try using:

Thanks!

How to tweet through Tweet button, but with my Text box ?

Instead of using the tweet button, you’ll want to use the Tweet Web Intent. Create a text box on your site, then once submitted transpose the user submitted-text to the tweet intent url and open it in a new window for your user. They’ll still have to confirm the tweet text one more time this way.

If you want a deeper integration, you’ll have to use OAuth.