FileOpen Error

[Forex Trader]

int coefs=0;
int coefss=2;
coefs= FileOpen("eurusd.csv",FILE_CSV|FILE_READ,',');
coefss= FileSize(coefs);
Print("ARMA TEST coefss", coefss);
Print("ARMA TEST coefs", coefs);
if(coefs<1)
{
Print("File my_data.dat not found, the last error is ", GetLastError());
return(false);
}

What causes -1 in coefs and coefss and error 4051 in getlasterror?

Thanks