However I had horrible crash when I once tried to take a active b complex
Maybe you started with too high a dose. Many people are very sensitive to these supplements and need to start with a tiny dose and increase slowly.
I can tolerate hydroxocobalamin, folic acid and inactive b6
Maybe you tolerate them because they are doing very little.
There does seem to be a significant number of people who can't process folic acid and inactive cobalamins. In my own case, parallel blood tests for folate and cobalamins and a urinary OAT test convinced me to try the active forms. I had only ever supplemented the small amounts of folic acid and cyanocobalamin in a standard B complex preparation. My blood tests showed very high folate and cobalamin (way above the normal range) but the OAT test showed significant functional deficiency of folate and B12.
I interpreted this to mean that the inactive vitamins were simply accumulating in blood and not getting into cells.
Once I started supplementing methyl folate and methyl and adenosyl B12 the OAT test normalised.
There is no reason to think that inability to process folic acid has anything to do with MTHFR snps. The problem is much more likely to lie with other aspects of folate metabolism and/or transport. It may not have anything to do with snps but rather with more general metabolic problems. Anyone with CFS/ME is likely to have plenty of these.