NSURLRequest *request=[NSURLRequest requestWithURL:[NSURL URLWithString:requestStr]
NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
NSLog(@"error: %@", [error localizedDescription]);
After hours of debugging we could narrow it down to the line of code that initialises the NSError. Setting it to nil did remove the crash. So make sure your code looks like this:
NSError *error = nil;
We are currently investigating more issues we have with code that ran perfectly fine in 3.x and now starts crashing with iOS4. The above line fixed approximately 80% of our problems.
Good luck making your apps ready for iOS4.