I think it may be...

because Montenegro has no currency of its own. Prior to the introduction of the euro in 2002, the Deutsche Mark was the de facto currency in all private and banking transactions. When the euro was introduced and the Deutsche Mark yielded, Montenegro began using the euro as well without any objections from the European Central Bank (ECB).
The European Commission and the ECB have since voiced their discontent over Montenegro's unilateral use of the euro on several occasions, with Amelia Torres, a spokesperson for the European Commission, saying "The conditions for the adoption of the euro are clear. That means, first and foremost, to be a member of the EU.? A statement attached to their Stabilisation and Association Agreement with the EU read: "unilateral introduction of the euro was not compatible with the Treaty."
The EU insists on the strict adherence to convergence criteria (such as spending at least 2 years in the ERMII system) which are not negotiable before euro adoption, but have not intervened to stop the unilateral use of the euro by Montenegro. The EU has raised concerns of Montenegro's state debt, which had risen to 57 percent of GDP by 2011.
Officials from the Central Bank of Montenegro have indicated on several occasions that the European institutions do expect them to strictly follow ERM rules, particularly because of their EU accession process. Nikola Fabris, the chief economist of the Central Bank of Montenegro, has said that situation was much different when they adopted the euro, and that other states which were considering unilaterally adopting the euro, such as Croatia and Bosnia, would face sanctions from the EU and have their accession process suspended if they went ahead.
On 17 December 2010 Montenegro was granted candidate status to join the European Union. The issue is expected to be resolved through the negotiations process. The ECB has stated that the implications of unilateral euro adoption "would be spelled out at the latest in the event of possible negotiations on EU accession."Diplomats have suggested that it's unlikely Montenegro will be forced to withdraw the euro from circulation in their country. Radoje Zugi, Montenegro's Minister of Finance, has stated that "it would be extremely economically irrational to return to our own currency and then later to again go back to the euro." Instead, he hopes that Montenegro will be permitted to keep the euro and has promised "the government of Montenegro, will adopt some certain elements, which should fulfill the conditions for further use of the euro; such as adopting fiscal rules."
Unlike official members of the Eurozone, Montenegro does not mint coins with a distinctive national design.

But I'm not sure.

Posted By: Steve in Holland, Mar 27, 12:56:07