为什么我加载软件包出现下面的警告啊？
> utils:::menuInstallPkgs()
试开URL’http://ftp.ctex.org/mirrors/CRAN ... 1/stringr_0.6.2.zip
Content type 'application/zip' length 75081 bytes (73 KB)
打开了URL
downloaded 5575 bytes
错
  无法打开链结
此外: 警告信息：
1: In download.file(url, destfile, method, mode = "wb", ...) :
  downloaded length 5575 != reported length 75081
2: In unzip(zipname, exdir = dest) : 从zip文件中抽取1时出了错
3: In read.dcf(file.path(pkgname, "DESCRIPTION"), c("Package", "Type")) :
  无法打开压缩文件'stringr/DESCRIPTION'，可能是因为'No such file or directory'