Summary:  Customer just upgraded system from 5.3.53053 and now receiving Error Downloading Signatures for Windows.

Issue:  Sometimes after upgrade the apppliance thinks a license is expired.  There are many different reasons for receiving this error so should not be the single stop action to resolve this error.  This is a quick trouble-shooting step that you can take if you upgraded to 5.4 and receive this error.

Resolution: Please look to your patching log.  Do you find something similiar to this log?

Error downloading Signatures for Windows.
Please check the server logs for more information.

From the log -
Dec 28, 2012 8:11:35 PM com.lumension.scr.client.SCRClient download
INFO: Processing Group : windows/x86_64-win7sp0.lst
sw_vers: not found
fopen(/kbox/kboxwww/patches/kace.plk,rb) failed
checksum error
/tmp/__PatchLink500388.cab: no valid cabinets found
Dec 28, 2012 8:11:35 PM com.lumension.scr.pojo.SecurityContent downloadPackage
SEVERE: Failed to import patch null
Dec 28, 2012 8:11:35 PM com.lumension.scr.pojo.SecurityContent downloadPackage
SEVERE: Failure return code PPX_ERROR_EXPIRED_LICENSE_KEY
Dec 28, 2012 8:11:35 PM com.lumension.scr.client.SCRClient process
SEVERE: Error Processing Content Download Request.null
Dec 28, 2012 8:11:35 PM com.lumension.scr.client.SCRClient process
INFO: System Configuration: ( {payload_folder=/kbox/kboxwww/patches, threshold=10737418240, MasterListFileName=/kbox/kboxwww/patches/WINDOWS_master.lst, force_refresh=false, keyFile=/kbox/kboxwww/patches/kace.plk, index=kbox3-ec.xml, folder=/kbox/kboxwww/patches, refresh_metadata=false, program=/kbox/bin/SCR/bin/, download_packages=false, payloadFolder=/kbox/kboxwww/patches/plp, listfiles_inclusive=/kbox/bin/SCR/bin/kaceconfig/listfiles_inclusive.lst, cacheResponseFolder=/kbox/bin/SCR/cacherequest, checkPayload=true, dist=ENGLISH, download_signatures=true, cacheRequestFolder=/kbox/bin/SCR/cacherequest, exclusions=/kbox/kboxwww/patches/exclusions.lst, configlog=/kbox/bin/SCR/logs/Windows-Config.log, platform=WINDOWS, arch=X86_64} )
[2012-12-28 20:11:35 -0500] KPatch [info] SCR Processing Complete
[Fri Dec 28 20:11:35 EST 2012] [notice] Exceptions(120:Lumension library encountered error processing content) occured while downloading signatures from CDN.Signatures might not be imported for Windows
[Fri Dec 28 20:11:35 EST 2012] [notice] No active subscriptions for Platform: mac
[Fri Dec 28 20:11:35 EST 2012] [notice] To: KaceAdmins@company from:KaceAdmins@company subject : K1000 - Patch Download Failed Msg: <font color='red'>Error</font> downloading Signatures for Windows.<br>
Please check the server logs for more information.

[Fri Dec 28 20:11:45 EST 2012] [notice] /kbox/kboxwww/patches//SCR_CONTENT.lst is empty. SCR did not return metadata info. Exiting.
[Fri Dec 28 20:11:45 EST 2012] [notice] kpatchsystem - Downloading package files
[Fri Dec 28 20:11:46 EST 2012] [notice] kpatchsystem - Complete.

Go to settings>patch settings.  Click to edit and the click save without changing anything.  This has been reported to resolve the issue.  You should be able to download patches now.