Xcode error while downloading files from sandbox

Question

I save the files as .txt files using the following code:

FILE* file; file = NULL; const char *filename = [newFilePath UTF8String]; file = fopen(filename, "wb"); 

However, when I load them from the Sandbox into Organizer, an error occurred:

Xcode detected an unexpected error (0xC011). The file exists at "/SourceCache/DVTiOSFrameworks/DVTiOSFrameworks-5053/DTDeviceKitBase/DTDKApplication.m:1340

Then only a small fraction of the files are downloaded.

Does anyone know why and how to solve this problem?