2388805 - Portal runtime error on logon page after system upgrade due to authschemes.xml file computation issue

After system upgrade and logging on Portal, you are getting a Portal runtime error with an Exception ID instead of normal Portal logon page.
From defaulttrace you can see below error corresponding to specific exception ID:
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#Error#com.sapportals.portal.prt.service.authenticationservice.AuthenticationService#
#EP-PIN-PRT#sap.com/com.sap.portal.runtime.system.authentication#C000AC1008D505B000000000000010BC#7358951000000004#sap.com/irj#com.sapportals.portal.prt.service.authenticationservice.AuthenticationService#Guest#0##E2075A9DA16B11E6C1610000007049E7#e2075a9da16b11e6c1610000007049e7##0#Thread[HTTP Worker [@707575056],5,Dedicated_Application_Thread]#Plain##
An error occured during authscheme computation.

#Error#com.sap.portal.prt.runtime#
#EP-PIN-PRT#tc~epbc~prtc~api#C000AC1008D505B000000001000010BC#7358951000000004#sap.com/com.sap.portal.runtime.system.hooks#com.sap.portal.prt.runtime#Guest#0##E2075A9DA16B11E6C1610000007049E7#e2075a9da16b11e6c1610000007049e7##0#Thread[HTTP Worker [@707575056],5,Dedicated_Application_Thread]#Plain##
<Exception ID> An error occurred in iView: N/A in component: N/A#
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SAP NetWeaver 7.3 ; SAP NetWeaver 7.4 ; SAP NetWeaver 7.5 ; SAP enhancement package 1 for SAP NetWeaver 7.3

authschemes.xml, portal runtime error, portal logon page, portal upgrade, custom logon screen , KBA , EP-PIN-PRT , Portal Runtime , Problem

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