Crystal reports 2011 exporting report having sub reports to excel

I have recently upgraded to crystal reports 2011 , but found crystal report engine problem when exporting to excel which has got subreport and in the subreport  having groups defined.IT gets hanged when calling reportdocument. export in visual studio 2010 c#

But when i do the same thing to export in pdf, works fine.

Any help is appreciated.

Thanks