使用AFNetWorking 上传字符串,提示:Request failed: 请求太大

我要把图片换成nsdata,然后再用base64encoding,把encoding后生成的字符串上传到
服务器,就出这个问题,
报错信息:err:Error Domain=com.alamofire.error.serialization.response Code=-1011 "Request failed: 请求太大 (413)"
我同事用的ASIHTTPRequest库就没问题,请问如何解决?
代码:

UIImage *img = [self createThumbnailWithSourceImge:sourceImg andNewSize:sz];

       data  = UIImageJPEGRepresentation(img, 0.01);
        NSString *encodedSTR  = [data base64Encoding];
                NSString *currentUrl = @"/app/b/test";
        NSString *urlStr = [NSString stringWithFormat:@"%@%@?picStr=%@",BASEURL,currentUrl,encodedSTR];
        NSURL *url = [NSURL URLWithString:urlStr];
        NSURLRequest *request = [NSURLRequest requestWithURL:url];
                 AFHTTPRequestOperation *op = [[AFHTTPRequestOperation alloc]initWithRequest:request];
    op.responseSerializer = [AFJSONResponseSerializer serializer];
    [op setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
//        NSLog(@"success:%@",responseObject);
        successBlock(responseObject);
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        failureBlock(error);
    }];
    [op start];


     //   [manager POST:urlStr parameters:nil
     //         success:^(AFHTTPRequestOperation *operation, id responseObject) {
        //          NSLog(@"success:%@",responseObject);
         //     } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
         //         NSLog(@"err:%@",error);
         //     }];
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