I can´t upload Attachments from my iPod touch 4G with iOS 6.1.6 on the phpBB.com Community.
Did you mean phpBB.com or are you actually talking about the MyBB community? They're an entirely separate organization using different software.
i was MyBB user for... one or two years.
Its just a tyo
This is a problem with the plupload plugin when viewing a 3.1 forum using iOS. The easiest fix seems to be to force single file selection in the case of mobile browsing or at least for iOS.
The issue that David mentioned is addressed in Plupload itself. In our case, because the button is hidden on load, Plupload can't determine the correct location of the "Add files" button. So, we have to refresh the plupload instance once the button is visible so that the position gets recalculated.
Also for reference: https://www.phpbb.com/community/viewtopic.php?f=466&t=2269746
On a related note I've applied the patch to my live 3.1 forum and can verify that it indeed fixes the issue. Nice work.