While reading [Experts Exchange](http://www.experts-exchange.com)(EE) Community Newsletter, I came across a new phrase. I'm trying to understand, what does ***crossed signals*** mean in this context?

**Excerpt from the Newsletter:**

> 
> **This time we mean it:** Call it ***crossed signals***. *xxxx*, one of Experts
>  Exchange's site administrators, was supposed to host a meet-up at *xxxx*
>  in Denver last week, but a mix-up in communications forced its
>  postponement to Thursday, .... If you're so inclined, feel free to
>  come bend his ear about anything EE; you can RSVP here; the beer is on
>  us. ...
> 
> 
> 

... and finally, what does the sentence "the beer is on us" mean?

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