The most likely cause is lack of memory. First, verify that your device has at least 1 GB (1024 MB) of memory to meet the minimum requirements. Second, note that any applications running in the background also consume memory. We recommend closing all background apps before running a test.
The 3DMark for Android v1.0.1 update included changes that should resolve this issue for 1 GB device models. Verify that you have the updated version. Devices with less than 1 GB are officially unsupported but may be able to run the tests if you untick "INCLUDE DEMO" in the settings.