You checked the No Update Property if it is set. You have checked if any Buscomp Read Only User Property for the primary Record. If still you are not able to find the reason why you are not able to change the Primary.
The reason may be Position Protection mechanism. Position Protection is a mechanism that protects against unauthorized changes within a MVG applet based on Positions. If Position Protection is active then changes can only be done by privileged persons or within certain views.
In Siebel previous version before 7.x, Position Protection mode can be disable but to a limited extent.
In Siebel version 7.x and above, this does not apply. Disabling Position Protection is handled by setting the 'MVG Set Primary Restricted: visibility_mvlink_name' user property to 'FALSE'.
Position Protection is active when:
- the view's Property Admin Mode is set to FALSE
- the multi-value field's (MVF) business component is set up with Position Team Ownership
- Visibility Emp MVField
- Visibility MVLink
- The Multi Value Field is based on Positions.