Hi, this is an issue I need help with!

The Operation too large error is because you are trying to perform a query that exceeds the governor limits established by Salesforce.  If you don't have limits on your model you may see this error.  If you have aggregate queries that need to process millions of records you may get this error.  

See these: 
https://help.salesforce.com/apex/HTViewSolution?id=000212083&language=en_US 
http://salesforce.stackexchange.com/questions/17862/counting-notes-crashes-with-operation-too-large-exceeded-20000-distinct-ids

You should start looking at models to determine if any are attempting to wade through lots of records.  If nothing is immediately apparent upon reviewing model configuration,  you can comment each model out in the xml and rerun the page to work it down to identify a particular model. 

Also you need to test these pages in the context of someone who does not have the “view all data” permission - as this impacts the processing required to return queries. 

Finally - make sure that your VF pages (used for overrides) are running in Read Only mode.  This mode allows for the retrieval of substantially more records.