Saw Anthony's review on SimpleClear and checked, indeed there is a problem concerning multiple browsingData methods can only be run one at a time.
(Would appreciate you could post in the 'Send feedback' area under 'Bugs' next time.)
I understand the problem and I'm currently trying to work out a solution.
EDIT: Actually as of current edit (3 days of a few hours of experimenting, 4 hours after post), the code is fixed as in no more errors. But I need to wait out on one question before I push out the update.
UPDATE: Went on to file a bug report at Chromium Issues.
20/6/13: The bug is fixed in Chromium builds (206917 onwards) but have yet to make it to the Chrome builds, will release the fixed extension when the bug fix hits official Chrome builds.
26/6/13: The bug fix comes with dev 29.0.1547.0, I'll push out the new version later tonight.
26/6/13: Looks like I can't put out tonight as my home broadband is down :(
27/6/13: Darn! No internet connection still. The technician will come by on Saturday, hopefully all goes well.