If the DOUBLE() function (which casts a string to a floating-point number) is given input with spaces in (such as " 1,234 ") an exception is thrown.
A temporary workaround is to remove the spaces before passing the parameter to the DOUBLE() function:
DOUBLE(SUBSTITUTE(A2, ' ', ''))
A CSV file illustrating the problem is at:
http://www.bbsrc.ac.uk/nmsruntime/saveasdialog.aspx?lID=6515&sID=12031