error creating a basic page when I create a simple basic page like About Us and I click Save Preview I get the errror ”The trimmed version of your post shows what your post looks like when promoted to the main page or when exported for syndication. You can insert the delimiter "" (without the quotes) to fine-tune where your post gets split.” How can I get rid of this?
saadlulu is right - this is a notice (not an error) provided by the core node module and relates to the preview functionality you have enabled. Are you trying to disable preview?

If you just want to disable the message, try the 'disable messages' module and make sure to heed the advice here and use the following wildcard:

The trimmed version of your post shows what your post looks like when promoted to the main page.*