OpenFOAM

Hi all!

I am trying to compute the sum of the concentration (c) field on the outlet patch using the following fuctionObject dictionary in controlDict:

functions
{
    outlet
    {
        type            surfaceFieldValue;
        libs            ("libfieldFunctionObjects.so");
        writeControl    timeStep;
        writeInterval   1;
        writeFields     no;
        surfaceFormat   vtk;
        enabled         true;
        log             true;
        fields          (c);
        regionType      patch;
        name            outlet;
        operation       sum;
    }
}

however, no matter what I change or if I try to code the functionObject directly in the controlDict, I keep getting the following error:

--> FOAM FATAL IO ERROR: 
error in IOstream "OSHA1stream.sinkFile_" for operation Ostream& operator<<(Ostream&, const word&)

file: OSHA1stream.sinkFile_ at line 0.

    From function virtual bool Foam::IOstream::check(const char*) const
    in file db/IOstreams/IOstreams/IOstream.C at line 96.

It seems that OF cannot open or write the result on the log file. Does anyone have any suggestion?