OS Error:"The Flow Fraction for Surface x in Surface Group LOW TEMP RADIANT VAR FLOW nameCEILINGS is too low * Flow fraction of 3E-004 is less than minimum criteria = 1.000000E-003''

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This error is reported when the surface is really small.

Go back into the Openstudio Sketchup Plugin and use the search function to search for Surface x. You will find a really small surface.

Delete the surface and unhide your model. Make sure that this did not delete another surface it was connected to (if it did, just redraw the surface by connecting two vertices).