Can you increase the max size of Rich Text fields? I'm unable to save an entry, and I'm getting an error saying that a Rich Text field is too long.

If I disable the entry, it saves fine, but when it's enabled, it doesn't save.

Can I increase the max size of a Rich Text field?
Under your Rich Text field's setting, there is a "Column Type" option that's set to text by default, which will hold about 64k worth of data.  You can change it to mediumtext, which will store about 16M worth of data.