I started using
showkeys in one of my documents and see this error
\pdfendlink ended up in different nesting level than \pdfstartlink
A bit of google suggests that this "happens when hyperref is used under pdftex and a citation splits across a page boundary". (See: http://tug.org/errors.html).
But this package is only useful at drafting stage where the text is changing frequently i.e. the chance of the error is high. Is there a general way to smoothly use