Here is the rating from 2010!
“Meanwhile, the Better Business Bureau in January slapped a D-minus rating on Trump U., a rating now under review after Trump U. objected. Trump Institute got an F in early 2009.”
http://www.nydailynews.com/news/trump-u-hit-complaints-paid-30g-return-article-1.446342
The implication from the Times is that the rating was specific to Trump University.
The information that I found had reasons listed and the only reason given was “Reason for this D- rating include: BBB concerns with the industry in which this business operates”.
There were 13 claims out of thousands of participants and all had been settles. I think the NY Times article is a hit piece.