i have used many2one fields in so many places in my custom module. It is woking fine on all others databases, but on only one datatbase, when i try to update module, it gives error: like Programming error: there is no primary key for reference table res_user 

Generates error on following code.

'session_started_by': many2one('res.users','Operator')

for the time i removed the above code, but later on it gives same errors on other line of code where i used many2one. I gues there is some problem with the database.

It updates without any error on other databases, problem occurs with only one database