"Decat" - is an adverb that requires a negative verb for correct semantics. For positive the correct adverb is "doar". EG: "Nu am decat 5 lei" - is correct but "Am decat 5 lei" is scratching both my ears and the Romanian grammar. In the positive case the expression should be "Am doar 5 lei". But the "meltenesque" population is using the wrong form... I am doomed to hear them.
As my reader Bogdan Alexandru remarked I have put a wrong example on my post. In fact the idea was the usage of the "la" Accusative preposition for expressing the Dative "I-am dat la fata" instead of "I-am dat fetei". The problem is that the substantive "fata" has an Nominative/Accusative form because of the preposition. In my example there is also a problem of accord for the gender - it was an ear scratching expression heard yesterday.
I am not a linguist but I like speaking and hearing a correct language. But what I hear around is just a "gipsy"-anization of the language based on the precarious education in the Romanian institutes. Language is in my opinion a sacred asset for a nation and should be guarded with all the possible energies.