Slow transfer from a Smartphone

Hi,
i use Airdroid 3 on my Android Phones. I´ve registered 5 Smartphones, 4 of them makes no Problems, but one has a Problem:
It is a Blackberry DTEK60. If i want to download a Picture or make anything else with airdroid on my Mac, the Transfer-Rate is extrem low. 1-2kb/sec is fast... And i am in my local wifi network.

At the same place i can transfer Datas from all other android Smartphones in high speed...
What could be the Problem?

Thank you for your help...
Regards
Andreas