What is EL Expression Unbalanced?

Here I got a web page developed using JSF 2.0. Anyhow I am not able to render the page correctly and following error shown on the page:

/thepage.xhtml @12,44 value="#{theBean.contactKey)" EL Expression Unbalanced: ... #{theBean.contactKey)

What is this error means? It took quite some time for me to understand this error message until I found out there is something not so right on the eval-expression construct, #{theBean.contactKey). There are 2 types of construct so far I read in the EL Expression book, either #{expr} or ${expr}. Thus there is no such thing #{expr).