I got the following error recently on slackin after days without any problem:

$ /usr/local/bin/slackin --interval 5000 --port 10000 domain xxxx
Thu Oct 08 2015 20:10:52 GMT+0200 (CEST) – fetching
Thu Oct 08 2015 20:10:52 GMT+0200 (CEST) – listening on *:10000
Thu Oct 08 2015 20:10:53 GMT+0200 (CEST) – ready
WARN: no logo configured
Thu Oct 08 2015 20:10:53 GMT+0200 (CEST) – online 6, total 29
Thu Oct 08 2015 20:10:58 GMT+0200 (CEST) – fetching
Thu Oct 08 2015 20:10:59 GMT+0200 (CEST) – Error: Invalid Slack response: 429
at SlackData.onres (/usr/local/lib/node_modules/slackin/node/slack.js:77:22)
at /usr/local/lib/node_modules/slackin/node/slack.js:41:17
at Request.callback (/usr/local/lib/node_modules/slackin/node_modules/superagent/lib/node/index.js:746:30)
at Request. (/usr/local/lib/node_modules/slackin/node_modules/superagent/lib/node/index.js:135:10)
at emitOne (events.js:77:13)
at Request.emit (events.js:169:7)
at IncomingMessage. (/usr/local/lib/node_modules/slackin/node_modules/superagent/lib/node/index.js:938:12)
at emitNone (events.js:72:20)
at IncomingMessage.emit (events.js:166:7)
at endReadableNT (_stream_readable.js:893:12)
Thu Oct 08 2015 20:10:59 GMT+0200 (CEST) – retrying
Thu Oct 08 2015 20:11:09 GMT+0200 (CEST) – fetching
Thu Oct 08 2015 20:11:09 GMT+0200 (CEST) – Error: Invalid Slack response: 429
at SlackData.onres (/usr/local/lib/node_modules/slackin/node/slack.js:77:22)
at /usr/local/lib/node_modules/slackin/node/slack.js:41:17
at Request.callback (/usr/local/lib/node_modules/slackin/node_modules/superagent/lib/node/index.js:746:30)
at Request. (/usr/local/lib/node_modules/slackin/node_modules/superagent/lib/node/index.js:135:10)
at emitOne (events.js:77:13)
at Request.emit (events.js:169:7)
at IncomingMessage. (/usr/local/lib/node_modules/slackin/node_modules/superagent/lib/node/index.js:938:12)
at emitNone (events.js:72:20)
at IncomingMessage.emit (events.js:166:7)
at endReadableNT (_stream_readable.js:893:12)
Thu Oct 08 2015 20:11:09 GMT+0200 (CEST) – retrying