What can I do? Schedule B is invalid for Electronic Filing. Please remove all preceding spaces or invalid characters. It won't let me correct and won't let me proceed.

It may be best to delete your form and then re-enter it without preceding or invalid characters.  The IRS is very particular about using special characters in their data.  It will come back as rejected just as a name / SSN mismatch would, and it could then get "stuck."  

How do I view and delete forms in TurboTax Online?

• Open or continue your return in TurboTax.
• In the left menu, select Tax Tools and then Tools.
• In the pop-up window Tool Center, choose Delete a form.
• Select Delete next to the form/schedule/worksheet in the list and follow the instructions.

Then, try clearing your cache.  

Your browser stores recently visited webpages as temporary files in a cache, which enables the pages to load more quickly when revisited.

However, a full or corrupted cache can cause problems in TurboTax, so sometimes you need to clear your cache (that is, remove these temporary files).

Here are the official instructions for the most popular browsers:

• Google Chrome
• Mozilla Firefox
• Microsoft Internet Explorer 11 (use the drop-down on the upper right corner of that page for earlier versions)
• Microsoft Edge

Apple's official support site doesn't appear to contain instructions for clearing the cache in Safari. Your best bet is to search the Internet for clear Safari cache or similar search terms.