Your problem could be caused by two possibilites
1) The key code unit (part of the car) has forgotten the individual blue
2) The blue key is duff.
The good news is that you have the Red key.
You can try reprogramming ALL the blue keys back into the system. If
that does not work then you will have to obtain a new blue key from you
Fiat dealer/other source and then reprogram that key into the system.
Sequence for reprogramming keys can be found on the Internet. When the
sequence is activated ALL blue key codes are wiped from the system so
you MUST have all blue keys present so they can be re-accepted by the
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