http://www.politicususa.com/2016/09/02/trump-foundation-claimed-10000-donation-exist.html

Trump Is The Corrupt Candidate With A Charity Problem Not Hillary Clinton 

In 24 hours, Fahrenthold has reported that Trump's foundation is seemingly guilty of a pay-to-play scam and false claims of giving on its tax forms. These are real scandals, unlike the accusations about the Clinton foundation.

Trump’s foundation on two fronts, one of which appears to be illegal.

Front one: Donald Trump’s Foundation claimed on its tax return forms that it gave $10,000.00 to The Giving Back Fund in 2008, but the organization says that donation does not exist, Fahrenthold reports. 

This is the third charity that told the Washington Post reporter that the Trump Foundation’s tax forms were wrong when claiming they gave them money. He said he gave them money but they got none. So this doesn’t look like a “mistake”. 

Now you know why he doesn't want to release his tax forms.