Many bloggers have complained of not being able to change to a new Blogger template or save an edited template. The error code they get is bX-cxyu7t. This has happened before and there is nothing to do but sit it out. I myself have tried and got he same error code
Hopefully you have sufficient patience.
Update 14 June 2008: Changing to a different browser is my favorite strategy when I have similar problems, but this time somehow I left it out. As you can see from the comments, one blogger managed to solve the problem by using a different browser.