Reading page layouts via REST returns 500 error with UNKNOWN_EXCEPTION error code for certain sobjects

Question

It seems to happen mainly on 3rd party plugins, but it is only happening on a small minority. Here's an example sobject from a Conga plugin: "APXTConga4__Conga_Composer_Settings__c". SObject describe shows that it is createable, updateable, deleteable, queryable, etc. It is also "layoutable"! But the only layouts I can read on it are search layouts. CompactLayoutable is false and lookupLayoutable is null.

So here are my questions:

1. Is there some hint in the sobject describe that I can use to know I'll get this exception when I try to read page layouts? (like maybe lookupLayoutable being null or some such?)
2. If answer to (1) is no, and I just need to handle the error, then is this object really createable? How are objects created when they have no page layouts?

Other entities: Financial_Data_Lock_Settings__c, LeadConverterFieldMap__c, OppRollupSettings__c, OrgOppsRTs__c

thanks! I'm on version 29.0

Answer 1

I don't have Conga installed to check, but I suspect these are all Custom Settings. You can use the customSetting property from the sObject description to verify this.

If this is the case it would explain the lack of page layout support.