Fresh install of MCPE 0.10.4 on an Android tablet. Starts up ok. Click Play and then New. Enter details of World and click Create World!
Message displayed: "My World" can't be opened.
Tried every possible combination of settings but makes no difference.

Tried on similar tablet and it works ok. Examined tablet storage by connecting to a PC.
Looked in \games\com.mojang\minecraftWorlds
All the worlds that we tried to create had folders containing files.
However, none of these worlds are listed in the game when Play is clicked.

Did same on other tablet and noticed that there were more files in each created world.
Copied some of these worlds to the non-working tablet. Started MCPE and clicked Play. Now shows the copied worlds in the list. Selected a world but still got the "My World" can't be opened message.

Ran PocketMine server on my PC. Both tablets show the server world in the list and when selected, they both connect and work as expected.
Issue appears to be in creating/loading local worlds.

Files in a world folder on "non-working" version:
======================================
db (folder)

• lost (folder)
• contains 17 x .log files numbered from 000003 to 000051, going up in steps of 3, plus MANIFEST-000001
• CURRENT
• LOCK
• LOG
• LOG.old
• MANIFEST-000001

Files in a world folder on "working" version:
==================================
level.dat
db (folder)

• 000005.ldb
• 000379.ldb
• 000380.ldb
• 000381.ldb
• 000382.ldb
• 000383.ldb
• 000385.ldb
• 000386.ldb
• CURRENT
• LOCK
• LOG
• LOG.old
• MANIFEST-000384

Both tablets are running Android KitKat 4.4.2 and the same version of MCPE (v0.10.4 alpha)