Description of problem:
I have devel version of Satellite 5.3.1 with CDN enabled (xml_dump_version 3.4) and I get ISE from hosted (rhn.redhat.com) during satellite-sync when I try to download first package from channel. The same action works in stage.
The ISE happen just before I should get redirect to CDN.
CDN on hosted should be enabled (ticket CRQ000000001365)

Tail of satellite-sync, with some additional information:
11:09:33 Diffing package metadata (what's missing locally?): rhel-x86_64-server-5
            ________________________________________
Diffing:    ######################################## - complete
11:09:42
11:09:42 Downloading rpm packages
11:09:42    Fetching any missing RPMs: rhel-x86_64-server-5 (5308)
DBG 5 rhel-x86_64-server-5 ('libIDL-devel', '0.8.7', '1.fc6', '', 'x86_64') 0
DBG2 self._uri: https://satellite.rhn.redhat.com/SAT
DBG3 params: ('<?xml version="1.0"?>\n<params>\n<param>\n<value><struct>\n<member>\n<name>username</name>\n<value><string>rhnse</string></value>\n</member>\n<member>\n<name>operating_system</name>\n<value><string>redhat-release</string></value>\n</member>\n<member>\n<name>description</name>\n<value><string>Initial Registration Parameters:\nOS: redhat-release\nRelease: 5Server\nCPU Arch: i686-redhat-linux</string></value>\n</member>\n<member>\n<name>checksum</name>\n<value><string>4b950986599694d89ca0dae1399e6549</string></value>\n</member>\n<member>\n<name>profile_name</name>\n<value><string>xen74.englab.brq.redhat.com</string></value>\n</member>\n<member>\n<name>system_id</name>\n<value><string>ID-1016692703</string></value>\n</member>\n<member>\n<name>architecture</name>\n<value><string>i686-redhat-linux</string></value>\n</member>\n<member>\n<name>os_release</name>\n<value><string>5Server</string></value>\n</member>\n<member>\n<name>fields</name>\n<value><array><data>\n<value><string>system_id</string></value>\n<value><string>os_release</string></value>\n<value><string>operating_system</string></value>\n<value><string>architecture</string></value>\n<value><string>username</string></value>\n<value><string>type</string></value>\n</data></array></value>\n</member>\n<member>\n<name>type</name>\n<value><string>REAL</string></value>\n</member>\n</struct></value>\n</param>\n</params>\n',), methodname: authentication.login
Connecting via https to satellite.rhn.redhat.com
Incoming headers:
        content-length : 593
        x-rhn-server-capability : registration.finish_message(1)=1, registration.remaining_subscriptions(1)=1, applet.has_base_channel(1)=1, registration.smbios(1)=1, registration.extended_update_support(1)=1, rhncfg.filetype.directory(1)=1, rhncfg.content.base64_decode(1)=1, registration.register_osad(1)=1, registration.delta_packages(1)=1, xmlrpc.packages.extended_profile(1)=1, xmlrpc.login.extra_data(1)=1
        x-rhn-proxy-version : 0
        x-transport-info : Extended Capabilities Transport (C) Red Hat, Inc (version 136589)
        x-rhn-client-version : 1
        server : Apache
        connection : close
        date : Tue, 26 Jan 2010 10:09:43 GMT
        content-type : text/xml
body: "<?xml version='1.0'?>\n<methodResponse>\n<params>\n<param>\n<value><struct>\n<member>\n<name>X-RHN-Auth-Expire-Offset</name>\n<value><string>7200.0</string></value>\n</member>\n<member>\n<name>X-RHN-Auth-User-Id</name>\n<value><string></string></value>\n</member>\n<member>\n<name>X-RHN-Auth</name>\n<value><string>pVmo+W1D7iaqEl7RJegP/Q==</string></value>\n</member>\n<member>\n<name>X-RHN-Auth-Server-Time</name>\n<value><string>1264500583.58</string></value>\n</member>\n<member>\n<name>X-RHN-Server-Id</name>\n<value><int>1016692703</int></value>\n</member>\n</struct></value>\n</param>\n</params>\n</methodResponse>\n"
DBG6 login_token {'X-RHN-Server-Id': 1016692703, 'X-RHN-Auth-Server-Time': '1264500583.58', 'X-RHN-Auth': 'pVmo+W1D7iaqEl7RJegP/Q==', 'X-RHN-Satellite-XML-Dump-Version': 3.3999999999999999, 'X-RHN-Auth-User-Id': '', 'X-RHN-Auth-Expire-Offset': '7200.0'}
DBG2 self._uri: https://satellite.rhn.redhat.com/SAT
DBG3 params: ('rhel-x86_64-server-5', 'libIDL-devel-0.8.7-1.fc6.x86_64.rpm'), methodname: getPackage
Connecting via https to satellite.rhn.redhat.com
DBG4 http: 500, fault 0
11:09:45 ERROR: http error code :500; fault code: 0;
+++ sending log as an email +++

SYNC ERROR: unhandled exception occurred:

(Check logs/email for potentially more detail)

<ProtocolError for satellite.rhn.redhat.com /SAT/$RHN/rhel-x86_64-server-5/getPackage/libIDL-devel-0.8.7-1.fc6.x86_64.rpm: 500 Internal Server Error>
<ProtocolError for satellite.rhn.redhat.com /SAT/$RHN/rhel-x86_64-server-5/getPackage/libIDL-devel-0.8.7-1.fc6.x86_64.rpm: 500 Internal Server Error>