使用Dropbox SDK为iOS上传文件,获取错误代码403

我正试图使用dropbox SDK for ios上传一个文件,我已经正确设置了框架,并与dropbox帐户链接,但现在当我试图上传文件时,我收到了这个错误:

[WARNING] DropboxSDK: error making request to /1/files_put/sandbox/DBApp.sqlite - (403) Forbidden
2013-08-28 15:07:12.418 MyApp[3761:c07] File upload failed with error - Error Domain=dropbox.com Code=403 "The operation couldn’t be completed. (dropbox.com error 403.)" UserInfo=0x11e77ef0 {sourcePath=/Users/Piero/Library/Application Support/iPhone Simulator/6.1/Applications/553ACC67-D119-44A9-B7E0-7188773AD496/Documents/DBApp.sqlite, destinationPath=/sandbox/DBApp.sqlite, error=Forbidden}

这是我使用的代码:

NSString *filename = @"DBApp.sqlite";
NSString *destDir = @"/";
NSString *oldPath = [[self applicationDocumentsDirectory] stringByAppendingPathComponent:@"DBApp.sqlite"];
[[self restClient] uploadFile:filename toPath:destDir withParentRev:nil fromPath:oldPath];

有人能帮我吗?