I came upon this problem because the site I wanted to access had server problems, meaning the website was down. When my code tried to access it again, it gave out this “Invalid use of SingleClientConnManager: connection still allocated” exception message.
My code uses Apache’s HttpClient 3rd party library and I thought at first calling the consumeContent() method of the HttpEntity class did the trick since I never even closed the InputStream when getting a reference to it. It did not.
Luckily, after much surfing I stumbled upon Jason Hudgin’s site where he created a convenience method that avoids this problem.