When I try to set view permissions on a page I get the following errors.

Cannot insert duplicate key row in object 'dbo.TabPermission' with unique index 'IX_TabPermission_Users'. The duplicate key value is (, 103, 3). The statement has been terminated.

I found bug DNN-4869 that references this behavior in 7.3  (this was an upgrade from 7.2.2 to 7.4.2) but there is no indication how to clear the error... Supposedly it was fixed in 7.3.0.164.

This is an error on about 20+ pages and I'm thinking of just wiping and resetting the permissions but I'm too rusty - can't remember how I used to do that safely (boy... getting old sucks!)

DNN-4869 refers to a different index, in your case it is referring to the user index, which should be filtered to records with userid not null.
you may drop and recreate the index by running the following script in Host > SQL:

IF EXISTS(SELECT * FROM sys.indexes WHERE name = N'IX_{objectQualifier}TabPermission_Users' AND object_id = OBJECT_ID(N'{objectQualifier}TabPermission'))
DROP INDEX [IX_{objectQualifier}TabPermission_Users] ON {databaseOwner}[{objectQualifier}TabPermission]
GO

-- make sure, table content meets requirements:
UPDATE      {databaseOwner}[{objectQualifier}TabPermission]           SET UserId = Null WHERE UserId = -1
UPDATE      {databaseOwner}[{objectQualifier}TabPermission]           SET RoleId = Null WHERE UserId Is Not Null
DELETE FROM {databaseOwner}[{objectQualifier}TabPermission]           WHERE RoleId                Is Not Null AND NOT RoleId                IN (SELECT RoleId                FROM {databaseOwner}[{objectQualifier}Roles]               )
DELETE FROM {databaseOwner}[{objectQualifier}TabPermission]           WHERE UserId                Is Not Null AND NOT UserId                IN (SELECT UserId                FROM {databaseOwner}[{objectQualifier}Users]               )
DELETE FROM {databaseOwner}[{objectQualifier}TabPermission]           WHERE TabId                 Is Null      OR NOT TabId                 IN (SELECT TabId                 FROM {databaseOwner}[{objectQualifier}Tabs]                )
DELETE FROM {databaseOwner}[{objectQualifier}TabPermission]           WHERE PermissionID          Is Null      OR NOT PermissionID          IN (SELECT PermissionID          FROM {databaseOwner}[{objectQualifier}Permission]          )
-- Delete duplicate records:
DELETE FROM {databaseOwner}[{objectQualifier}TabPermission]     	  WHERE TabPermissionID NOT IN
 (SELECT Min(TabPermissionID) FROM {databaseOwner}[{objectQualifier}TabPermission] GROUP BY TabID, PermissionID, RoleID, UserID)
-- Make sure, there are no records with userID and roleID assigned any more:
DELETE FROM {databaseOwner}[{objectQualifier}TabPermission] 
	WHERE (UserID IS Not Null AND RoleID IS Not Null)
	OR	  (UserID IS     Null AND RoleID IS     Null)
GO

CREATE UNIQUE NONCLUSTERED INDEX IX_{objectQualifier}TabPermission_Users ON {databaseOwner}[{objectQualifier}TabPermission]
(UserID, TabID, PermissionID)
INCLUDE (AllowAccess)
WHERE UserID IS NOT Null
GO