404 error when attempting to save draft.

When I attempt to save a post draft and the body of the draft has a line break </br> or a new line in the visual mode of the editor, I recieve a 404 error.

If I disable the security mod, I cannot log in or out.

I have: uninstalled and trashed all plugins associated with tinyMCE. same problem.

As an example, if the body of the post is:
“test” – draft saves

If the body of the post is”
“test
test” – receive 404 error.

I have run a series of letters out 1000 places with no line break and the draft will save.

The problem first manifest as the body of text failing to wrap at the end of the window. Somehow I straightened that out by using the html editor. Don’t know how it was straightened out.

Can someone offer advise, or guide me before I toss the entire installation. What scripts do I need to check or replace, what additional trouble shooting steps can I take?

[ Please don’t bump, it’s not permitted here. ]