Importing Twitter user follower count into Google Spreadsheet using importXML

I have a Google Spreadsheet with a column of Twitter user handles (without the "@"). I'm trying to get a follower count using the following formula:

=importXML("http://twitter.com/"&A1,"//a[@data-nav='followers']")

where the user handle is in column A, but the spreadsheet returns

Error: Imported Xml content can not be parsed.

Any help would be appreciated!

Thanks in advance!