m2eclipse:Network connection problems encountered during search

为何更方便地使用Maven，选择安装m2eclipse插件，在官网http://m2eclipse.sonatype.org/installing-m2eclipse.html页面找到了更新地址：http://m2eclipse.sonatype.org/sites/m2e。

跟平常安装eclipse插件一样，输入地址，单击【Finish】时，进度条没走多少，就报了：Network connection problems encountered during search的错误提示。查看了detail信息，显示：
Network connection problems encountered during search.
Unable to access “http://m2eclipse.sonatype.org/sites/m2e/”.
Error parsing site stream. [White spaces are required between publicId and systemId.]
White spaces are required between publicId and systemId.
Error parsing site stream. [White spaces are required between publicId and systemId.]
White spaces are required between publicId and systemId.

感觉奇怪，怎么http://m2eclipse.sonatype.org/sites/m2e访问不了，用浏览器访问该地址，可以打开，如下所示：

有四个目录，其目录名也表明了m2eclipse的版本信息，分别有0.10.0.20100209-0800、0.10.2.20100623-1649、0.12.0.20101115-1102和0.12.1.20110112-1712，最后使用http://m2eclipse.sonatype.org/sites/m2e/0.10.0.20100209-0800/作为m2eclipse的更新地址，安装过程未出现问题，而对于其他三个目录，则依然报Network connection problems encountered during search的错误，不太清楚是啥原因，在Google查找也未找到具体的解决方法。

安装后，提示重新启动eclipse，可以通过菜单【Help】-【About Eclipse Platform】查看是否安装成功，成功的话，窗口会有一个M2的图标。此后，菜单【File】-【New Project】中将出现如下选项：