I think these two errors are unrelated. To me this reads like an issue with a missing file/directory in the generated virtual filesystem that the page is running on. Did you build from source? (or would you be able to?) If so, I wonder what the value of the path AdditionalDir is there? Given that it has a reference to “AddPluginDirectory” there, does the project use some plugins? Does a project without any plugins export and run correctly? Does this project run correctly in asm.js?
I think you should be able to re-enable IndexedDB by hand-editing the .html file and setting the boolean variable controlling IndexedDB to true. Iirc IndexedDB was temporarily disabled in that preview version due to a yet unresolved bug.