I have an APEX ControllerExtension class which overrides the Edit button.  To make life easy for me, I use a Dynamic SOQL statement to fetch all columns from the Opportunity sObject so they are available for display in the VF page should I need them

That is, I create a SOQL statement of the form:

'select field1,field2, ...fieldn from Opportunity where id = :oppId'

One of my fieldx is a formula field using this formula:

'First name Last name= ' & $User.FirstName & ' ' & $User.LastName & BR() &
'User.UserType= ' & TEXT($User.UserType) & BR() &
'UserRole.Name=' & $UserRole.Name & BR() &
'UserRole.PortalType=' & TEXT($UserRole.PortalType) & BR() &
'Profile.LicenseType=' & TEXT($Profile.LicenseType) & BR()

If this fieldx is included in either a dynamic SOQL or static SOQL expression, at run time, when executed from the Partner Portal by a partner Portal user, I get:

System.Exception: Internal Salesforce.com Query Error

and not much else.

Obviously, there is something this formula field does that messes up the SOQL call -- although the field displays fine on the standard controller user interface detail page (View).

I selectively commented out parts of the formula to determine which parts cause the Internal Salesforce.com Query Error

TEXT($User.UserType) - If present in the formula field, Internal Salesforce.com Query Error occurs

TEXT($UserRole.PortalType)  - If present in the formula field, Internal Salesforce.com Query Error occurs

All other expressions in the formula field don't cause an error.

I can work around this particular problem but in general, any sObject field should be queryable through SOQL and not depend on the formula expression.  Why it works through the standard controller UI and not through a controller extension SOQl (static or dynamic) is unknown.

Hopefully, this will help someone out in the future