Problem med fstream

Heysa, jeg har noget bøvl med noget kode:

        this->lastupdatefile = new fstream("lastupdatefile.txt", ios::in | ios::out );
       
        if(!(this->lastupdatefile))
        {
            cout << "(StatCalc::StatCalc)\t\t Error........reading lastupdatefile" << endl;
            exit(1);
        }
        char buf[100] = { 0 };

        // Denne linje virker! Skriver "abe" i filen
    this->lastupdatefile->write("abe",3);

        this->lastupdatefile->seekg(0);
        this->lastupdatefile->read( reinterpret_cast<char *>(&(this->lastupdatetime)), 4 );
       
    if(!this->lastupdatefile->eof() && this->lastupdatetime > 0)
        {
            strftime(buf, 99, "%T", localtime((const time_t *)&(this->lastupdatetime)));
           
            cout << "(StatCalc::StatCalc)\t\t Timestamp have been read succesfully! got: " << buf << " from file" << endl;
        }
        else
        {
            this->lastupdatefile->seekp(4);
                //Denne linjer virker IKKE!
        this->lastupdatefile->write("abe",3);

           
            this->lastupdatetime = time(0)-(60*60*24*7);    //Start with time 1 week ago
            strftime(buf, 99, "%T", localtime((const time_t *)&(this->lastupdatetime)));
           
            this->lastupdatefile->seekp(0);
            this->lastupdatefile->write( reinterpret_cast<const char *>(&this->lastupdatetime), sizeof(this->lastupdatetime) );
           
            cout << "(StatCalc::StatCalc)\t\t Timestamp have been manually! set - to enable readings of 24 hours data pre the last update time: " << endl;
            cout << "(StatCalc::StatCalc)\t\t The new offset for MySql query is: " << buf << " as starting time" << endl;
        }

De to kommentarer indsat ved write() er mit spørgsmål. Hvorfor virker den ene? Og den anden ikke?