PSOFT : Blank Pages in PIA after Upgrading to PT 8.5x

ISSUE :
Pages not being loaded when clicking on Content refs of Folders on the left hand menu or PT8.5x top navigation. i.e. on logging in PS left hand menu appears but on clicking on any Crefs of folder the blank page is displayed.
We faced this issue when we took the projects from 8.48.19 to our new upgraded 8.51.06.

CAUSE : 
From PT 8.50 "DEFAULT TEMPLATE" value "Usage Type" was changed from "Frame Template" to "Inline frame template".

SOLUTION :

To resolve the issue do the following.

i.e. Navigate to Portal Administration->Navigation->Structure and Content.
Select Portal Objects->Templates
Edit "8.50 default template".
Change "Usage Type" from "Frame Template" to "Inline frame template".
Save.
Reboot the web and app servers to have this change take affect.

IF you can't check/change this setting via PIA please issue the following query:

select * from PSPRSMDEFN
WHERE PORTAL_OBJNAME = 'DEFAULT_TEMPLATE' AND PORTAL_REFTYPE = 'C'
AND PORTAL_PRNTOBJNAME = 'PORTAL_TEMPLATES' AND PORTAL_CREF_USGT = 'FRMT'
AND PORTAL_URI_SEG1 = 'WEBLIB_PT_NAV'
AND PORTAL_URI_SEG2 = 'ISCRIPT1'
AND PORTAL_URI_SEG3 = 'FieldFormula';

If the PORTAL_CREF_USGT field value is "FRMT", then the following sql statement needs to be run to change the PORTAL_CREF_USGT value to "IFRM".

UPDATE PSPRSMDEFN SET PORTAL_CREF_USGT = 'IFRM'
WHERE PORTAL_NAME = 'XXXX_SITE_PORTAL_NAME' AND PORTAL_OBJNAME = 'DEFAULT_TEMPLATE' AND PORTAL_REFTYPE = 'C'
AND PORTAL_PRNTOBJNAME = 'PORTAL_TEMPLATES' AND PORTAL_CREF_USGT = 'FRMT'
AND PORTAL_URI_SEG1 = 'WEBLIB_PT_NAV'
AND PORTAL_URI_SEG2 = 'ISCRIPT1'
AND PORTAL_URI_SEG3 = 'FieldFormula';

Where 'XXXX_SITE_PORTAL_NAME' is the PORTAL_NAME value from the select statement.

After making the SQL updates,

Bring down appserver and webserver, clear both appserver/webserver cache