SharePoint 2010 published Inforpath forms opening error(the file is not a valid xml document. DTD is prohibited. Line 2, position 9)

Hi,

we have set of published inforpath forms in SharePoint 2010 CA. we are using these forms with a list in a site collection. these forms were working ok till couple of days ago, but now it is giving an error when trying to open in client application. the error message says,

"form template: XXXXXXXXXXXXXXXX.xsn

the file is not a valid xml document. DTD is prohibited. Line 2, position 9. "

we removed and republished these forms but that didn't help.

can someone please give any solution to fix this issue?

Thanks & Regards.