Getting 'bad file number' error writing to device driver

I am trying to write to mydriver but get a 'Bad file number' error. int fd = open("/dev/mydriver",O_RDWR); this opens successfully as fd is not -1. ssize_t bytesToWrite = strlen(buf); value is: bytesToWrite 28 ssize_t bytesWritten = write(fd,buf,bytesToWrite); value is: bytesWritten -1 __android_log_print(ANDROID_LOG_INFO,__FILE__,"ANIL strerror(errno) %s", strerror(errno)); value is: strerror(errno) Bad file number Any help appreciated. Anil