Client 1: When touching the chart with the palm of my hand I get a force close dialog because of an IllegalArgumentException. I was able to reproduce this behavior on your example app that I downloaded from the Google Play store. It was reproduced on 2 out of 6 devices. In these 2 devices it will happen every time I try.

Reproduced on (and reports were sent to you):
Samsung Nexus S (small screen).
Motorola Xoom (tablet).

Did not happen on:
Samsung Galaxy S2.
Sony Ericsson Xperia LT18i.
Samsung tablet GT-P7510.
Asus Transformer Prime TF201.

Client 2: It seem to happen when i touch 2 different places in the chart very fast after each other. I am able to reproduce the problem every time by touching and not releasing the chart with my index finger (with your whole finger not with the top of your finger).I tested it on the Line and Bar chart. I am getting this problem on the Motorola Xoom and the Motorola Xoom 2. Android version : 4.0.4

there is a chance that you are calling the following code in your onTouch;

event.getX()

which is probably causing errors

Steema: Not reproduced with Nexus 4, Nexus 7 (2012), Motorola Defy (Android 2.1) and Samsung Galaxy Ace (Android 2.3.6). Both Nexus devices tested used Android 4.3.