Getting the ever helpful "Authorization Required" page.  Admin Preview mode is enabled, no error message.  Log file is written, but no errors whatsoever.  Can anyone tell me what exactly would next steps be in troubleshooting this?

19.0 APEX_CODE,DEBUG;APEX_PROFILING,INFO;CALLOUT,INFO;DB,INFO;VALIDATION,INFO;WORKFLOW,INFO
23:04:49.160|EXECUTION_STARTED
23:04:49.160|CODE_UNIT_STARTED|[EXTERNAL]|066300000004viE|VF: /apex/Unauthorized
23:04:49.160|CODE_UNIT_STARTED|[EXTERNAL]|01p30000000CRPs|PortalMainController <init>
23:04:49.163|METHOD_ENTRY|[62]|MAP.get(ANY)
23:04:49.163|METHOD_ENTRY|[62]|System.PageReference.getParameters()
23:04:49.163|METHOD_ENTRY|[62]|ApexPages.currentPage()
23:04:49.164|METHOD_EXIT|[62]|ApexPages.currentPage()
23:04:49.164|METHOD_EXIT|[62]|System.PageReference.getParameters()
23:04:49.164|METHOD_EXIT|[62]|MAP.get(ANY)
23:04:49.164|METHOD_ENTRY|[80]|01p30000000CRPs|PortalMainController.getUrlParam(String)
23:04:49.164|METHOD_ENTRY|[120]|MAP.get(ANY)
23:04:49.164|METHOD_ENTRY|[120]|System.PageReference.getParameters()
23:04:49.164|METHOD_ENTRY|[120]|ApexPages.currentPage()
23:04:49.164|METHOD_EXIT|[120]|ApexPages.currentPage()
23:04:49.164|METHOD_EXIT|[120]|System.PageReference.getParameters()
23:04:49.164|METHOD_EXIT|[120]|MAP.get(ANY)
23:04:49.164|METHOD_EXIT|[80]|PortalMainController.getUrlParam(String)
23:04:49.167|METHOD_ENTRY|[5]|01p30000000CRPs|PortalMainController.retrieveAlertsToShow()
23:04:49.167|METHOD_ENTRY|[20]|Database.query(String)
23:04:49.170|SOQL_EXECUTE_BEGIN|[20]|Aggregations:0|select ID, knowledgearticleid, Localized_Title__c from Alert__kav where PublishStatus = 'online' and IsVisibleInPkb = true limit 10
23:04:49.178|SOQL_EXECUTE_END|[20]|Rows:2
23:04:49.178|METHOD_EXIT|[20]|Database.query(String)
23:04:49.178|METHOD_ENTRY|[21]|LIST.size()
23:04:49.178|METHOD_EXIT|[21]|LIST.size()
23:04:49.178|METHOD_EXIT|[5]|PortalMainController.retrieveAlertsToShow()
23:04:49.178|METHOD_ENTRY|[6]|LIST.size()
23:04:49.178|METHOD_EXIT|[6]|LIST.size()
23:04:49.178|CODE_UNIT_FINISHED|PortalMainController <init>
23:04:49.179|CODE_UNIT_STARTED|[EXTERNAL]|01p30000000CRPs|PortalMainController get(SiteUrlString)
23:04:49.179|CODE_UNIT_STARTED|[EXTERNAL]|01p30000000CRPs|PortalMainController invoke(getSiteUrlString)
23:04:49.180|METHOD_ENTRY|[31]|system.Site.getCustomWebAddress()
23:04:49.180|METHOD_EXIT|[31]|system.Site.getCustomWebAddress()
23:04:49.180|METHOD_ENTRY|[33]|system.Site.getCustomWebAddress()
23:04:49.180|METHOD_EXIT|[33]|system.Site.getCustomWebAddress()
23:04:49.180|CODE_UNIT_FINISHED|PortalMainController invoke(getSiteUrlString)
23:04:49.180|CODE_UNIT_FINISHED|PortalMainController get(SiteUrlString)
23:04:49.181|CODE_UNIT_STARTED|[EXTERNAL]|01p30000000CRPs|PortalMainController get(SelfServiceHomePage)
23:04:49.181|CODE_UNIT_STARTED|[EXTERNAL]|01p30000000CRPs|PortalMainController invoke(getSelfServiceHomePage)
23:04:49.181|CODE_UNIT_FINISHED|PortalMainController invoke(getSelfServiceHomePage)
23:04:49.181|CODE_UNIT_FINISHED|PortalMainController get(SelfServiceHomePage)
23:04:49.212|CUMULATIVE_LIMIT_USAGE
23:04:49.212|LIMIT_USAGE_FOR_NS|(default)|
  Number of SOQL queries: 1 out of 100
  Number of query rows: 2 out of 10000
  Number of SOSL queries: 0 out of 20
  Number of DML statements: 0 out of 100
  Number of DML rows: 0 out of 10000
  Number of script statements: 66 out of 200000
  Maximum heap size: 0 out of 3000000
  Number of callouts: 0 out of 10
  Number of Email Invocations: 0 out of 10
  Number of fields describes: 0 out of 100
  Number of record type describes: 0 out of 100
  Number of child relationships describes: 0 out of 100
  Number of picklist describes: 0 out of 100
  Number of future calls: 0 out of 10
  Number of find similar calls: 0 out of 10
  Number of System.runAs() invocations: 0 out of 20

23:04:49.212|CUMULATIVE_LIMIT_USAGE_END

23:04:49.212|CODE_UNIT_FINISHED|VF: /apex/Unauthorized
23:04:49.212|EXECUTION_FINISHED

As you can see, at the very end, it does some kind of auto-redirect to /apex/unauthorized.  the URL itself will render as the portal "frontdoor" URL, like

https://logmein.lmisupport.cs3.force.com/portal/secur/frontdoor.jsp?cshc=0000000SmHV00000000elr&portalId=06030000000KLOj&refURL=https%253A%252F%252Flogmein.lmisupport.cs3.force.com%252Fportal%252Fsecur%252Ffrontdoor.jsp&retURL=%252Fportal%252Fapex%252Fportalcasedetail&sid=00DQ00000000elr%2521ARsAQPMRBgvnE_sjnWsrc8aZgq857bO3C84ObcZOp4dOrmnM2CHLBcyfp5ufh64L4XCjMfffMFKQDVo07Ua7JbtgmA1WumAlSDU&untethered=

All VF pages required are granted for Site pages, in Public Access Settings, and for the Profile of the Portal User.  Same goes for all objects and fields referenced in the pages, for all 3 "layers".

 Getting extremely frustrated with the lack of ability to troubleshoot issues with Sites...:(