删除mongo分片collection失败

在中止balancer以后，备份整个分片库，而后启用balancer，删除分片集合并重建。遇到如下报错：

mongos> db.businessInfo.drop();
2016-08-14T09:06:58.324+0800 E QUERY    Error: drop failed: {
"code" : 13331,
"ok" : 0,
"errmsg" : "exception: collection's metadata is undergoing changes. Please try again."
}
    at Error (<anonymous>)
    at DBCollection.drop (src/mongo/shell/collection.js:620:15)
    at (shell):1:12 at src/mongo/shell/collection.js:620

理了一下逻辑，应该先drop sharding collection而后再启用balancer.