Question about IgG & IgM cross reactivity - (Apr/11/2014 )

I use a standard ELISA looking for antibodies to glycolipds, patients have either IgG or IgM antibodies but it is observed that  a patient with an IgM antibody will cross react with IgG.  This is a false positive. 

How can I stop this cross reaction ?

There are methods for eliminating cross-reactions such as described here http://jcm.asm.org/content/43/4/1944.full but also in this paper it says that none of them proved effective. What did you try ?