How to set 'pager.offset' in struts2 action?

[red phoenix]

I use struts2 and Pager Taglib2.0, in jsp file,it has a parameter,like
follows:
<input type="hidden" name="pager.offset" value="<%= offset %>">

when I run above code,it raise warning message:
Warn: ParametersInterceptor - [setParameters]: Unexpected Exception caught
setting 'pager.offset' on 'class test.ArticleAction: Error setting
expression 'pager.offset' with value '[Ljava.lang.String;@16b69d7'

I want to know how to set 'pager.offset'  in struts2 action?

Thanks!