ASP.NET Ajax client-side framework failed to load for Update Panel

I've googled through out and still couldn't find answer. The website is .net 2.0 and runs in intranet mode just fine for years throughhttp mode. Recently we need to allow outside users to access it via VPN. The problem is they will encounter

ASP.NET Ajax client-side framework failed to load.

Clicking on the link WebResource shows typical js code content. Clicking on ScriptResource.axd shows weird character �����������

<script  src="/+CSCO+d6756767633A2F2F66666E66696966662E66666E2E70622E666E61676E2D70796E656E2E706E2E6866++/App123/WebResource.axd?d=GS1f_TgsgIi2JZKN84jkVW_nV8Oe5ryScBw_7GLdGx5XOmnt08CpQ3B6p8DbBkgDp2FHOJ0_XTBW2phixRzhyVrbx7A1&amp;t=635294807132453548" type="text/javascript" ></script ><script id='CSCO_GHOST' language='JavaScript'>CSCO_seppuku();CSCO_WebVPN["flush"]();</script><script  src="/+CSCO+d6756767633A2F2F66666E66696966662E66666E2E70622E666E61676E2D70796E656E2E706E2E6866++/App123/ScriptResource.axd?d=Bwb1UcEtzvgLwhaBfFEOpJVuscFDJodCqux6bZN6v3D4yzqNEmS3rqxFd-R8q9SEATok5iEW5w1Rw9pWeq-gnHZ6d4G2XyrnmTmXRIRxh5teIT0X296elr5NqaONllCR8MC1jQ2&amp;t=ffffffffec54f2d7" type="text/javascript" ></script ><script id='CSCO_GHOST' language='JavaScript'>CSCO_seppuku();CSCO_WebVPN["flush"]();</script><script  type="text/javascript" >
//<![CDATA[
if (typeof(Sys) === 'undefined') 

When the site run through CISCO vpn, the URL is rewritten in this format. I don't know whether because it's https so it encrypts the scriptresource content.

https://xx.xxx.xxx/+CSCO+10756767633A2F2F66666E66696966662E666662E6866++/App123/-CSCO-30--default.aspx