Thanks a lot exact target for this helpful error:
Unable to generate preview:
A_SCRIPTINGA scripting error has occurred.
An error occurred when attempting to parse HtmlEmailBody content for HTML content.
MemberID: 1234151
JobID: 0
ListID: 123423
Content Begins With: %%[
Not only that, but you have to
close the editor window,click a checkbox,click send preview,click a listyou want to use to generate the email,click the email addressyou want to use to generate the email,then hit previewto find out that there is a problem.