Hi everyone, I am working with streams and sockets in iPhone SDK 3.1.3 the issue is when the program accept a callback and I want to handle this writestream callback the following error is triggered " Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: ' -[NSCFData writeStreamHandleEvent:]: unrecognized selector sent to instance 0x17bc70'" But I don't know how to solve it because everything seems fine. Even when I run the debugger there is no error the program works. Any hint here will help! The code of the callback is: void myWriteStreamCallBack (CFWriteStreamRef stream, CFStreamEventType eventType, void *info){ NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; Connection *handlerEv = [(Connection *)info retain] autorelease]; [handlerEv writeStreamHandleEvent:eventType]; [pool release]; } The code of the writeStreamHandleEvent: - (void)writeStreamHandleEvent:(CFStreamEventType) eventType{ switch(eventType) { case kCFStreamEventOpenCompleted: writeStreamOpen = YES; break; case kCFStreamEventCanAcceptBytes: NSLog(@"Writing in the stream"); [self writeOutgoingBufferToStream]; break; case kCFStreamEventErrorOccurred: error = CFWriteStreamGetError(writeStream); fprintf(stderr, "CFReadStreamGetError returned (%ld, %ld)\n", error.domain, error.error); CFWriteStreamUnscheduleFromRunLoop(writeStream, CFRunLoopGetCurrent(),kCFRunLoopCommonModes); CFWriteStreamClose(writeStream); CFRelease(writeStream); break; case kCFStreamEventEndEncountered: CFWriteStreamUnscheduleFromRunLoop(writeStream, CFRunLoopGetCurrent(),kCFRunLoopCommonModes); CFWriteStreamClose(writeStream); CFRelease(writeStream); break; } } The code of the stream configuration: CFSocketContext ctx = {0, self, nil, nil, nil}; CFWriteStreamSetClient (writeStream,registeredEvents, (CFWriteStreamClientCallBack)&myWriteStreamCallBack,(CFStreamClientContext *)(&ctx) ); CFWriteStreamScheduleWithRunLoop (writeStream, CFRunLoopGetCurrent(), kCFRunLoopDefaultMode); You can see that there is nothing strange!, well at least I don't see it. Thank you in advance.