Multispace 2006. Cranking but not starting!

My Multispace desire has developed intermittent starting problems. Some days it's fine and other days it just cranks but wont start. As if it's not recognising the the key.

I've been told it may be something to do with my spare key ( i lost the main key). Its works fine for months then I get this problem 

Could it be at the ignition barrel end where it's not picking up the transponder signal. 

Any advice would be gratefully received.

Thanks