FAILURE OF DISPATCH TO ADVISE ATC OF INOP FMS CAUSES E190 TO BE UNABLE TO DEVIATE MILITARY RESTRICTED AREA WHILE REMAINING IN REQUIRED CLASS I AIRSPACE.

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UPON ARR AT THE ACFT; WE LEARNED THAT THE ACFT HAD A NEW MEL FOR AN INOP FMS. UPON REVIEW OF THE MEL WE HAD CONCERNS ABOUT AN INOP FMS AND THE POSSIBILITY THAT DEVS ALONG OUR RTE MAY CAUSE ENTRY INTO CLASS II NAV AIRSPACE. THE MEL PROHIBITED ENTRY INTO CLASS II NAV AIRSPACE AND PRESCRIBED THAT DISPATCH VERIFIED THE SUITABILITY OF THE RTE. THE CAPT RAISED HIS CONCERNS WITH DISPATCH AND MAINT AND WAS ASSURED THAT ATC WOULD BE CONTACTED AS TO OUR FLT PLAN NAV SUFFIX AND THAT ANY DEVS FROM THE RTE WOULD BE WELL WITHIN CLASS I AIRSPACE. WE FELT ASSURED THAT ATC WAS NOTIFIED OF OUR LIMITATION FOR DEVS AND OF OUR NAV SUFFIX. AFTER PROCEEDING ENRTE WE WERE HANDED OFF FROM ZMA TO HAVANA CTR. WE CHKED IN WITH HAVANA AND NOTIFIED THEM WE WERE NEGATIVE RNAV. SHORTLY AFTER BEING IN CONTACT WITH HAVANA WE WERE NOTIFIED THAT A MIL WARNING AREA WAS ACTIVE AND TO PROCEED DIRECT TO CANOA. WE ADVISED THEM THAT WE BELIEVED TO BE ON COURSE. THEN; WE WERE ASKED TO RECONTACT ZMA. WE HAD NO INDICATION THAT THERE WAS AN ISSUE UNTIL CONTACTING ZMA; WHICH ADVISED US TO FLY A S HDG AND SQUAWK EMER. WE COMPLIED IMMEDIATELY WITH THE REQUEST AND LEARNED THAT THEY SHOWED US WITHIN AN ACTIVE MIL AIRSPACE. WE EXPLAINED THAT OUR VOR'S SHOWED US TO BE ON COURSE AND RESTATED THAT WE WERE NEGATIVE RNAV. MIAMI THEN ASKED US TO SQUAWK NORMAL; CONTACT HAVANA CTR AGAIN AND RESTATE OUR NAV LIMITATION. AFTER BEING IN CONTACT WITH HAVANA; A SIGNIFICANT BARRIER TO COM DEVELOPED AS WE WERE UNABLE TO EXPLAIN TO THE CTLR THAT WE WERE NEGATIVE 'RNAV; INS; FMS' AND THAT WE NEEDED TO STAY ON AN ESTABLISHED AIRWAY OR INTERCEPT A RADIAL. THE CTLR SEEMED TO THINK THAT WE WERE DISREGARDING INSTRUCTIONS WHEN ASKED TO PROCEED TO NOSAT. WE ASKED TO BE GIVEN A HDG TO INTERCEPT A RADIAL TO INTERCEPT THE AIRWAY TO PROCEED TO CUN. EVENTUALLY WE WERE ABLE TO INTERCEPT THE AIRWAY AND PROCEEDED UNEVENTFULLY. IT NOW APPEARS; BASED ON ANALYSIS FROM OUR SAFETY TEAM; THAT DISPATCH DID NOT PROPERLY VERIFY THE SUITABILITY OF OUR RTE OR COORD WITH ATC TO THE EXTENT WE WERE LED TO BELIEVE. OUR DECISION MAKING REGARDING THE ACCEPTANCE OF THE ACFT AND RTE; AS WELL AS THE MEL; WOULD HAVE BEEN DIFFERENT WITH MORE ACCURATE INFO. FOR A CORRECTIVE ACTION; I WOULD HESITATE TO TAKE AN ACFT WITH NEGATIVE RNAV ABILITY INTO FOREIGN AIRSPACE WHERE THE POSSIBILITY OF COM DIFFICULTIES AND THE POTENTIAL FOR ENTRY INTO MIL OR CLASS II AIRSPACE.