SQL database : relationship constraint error

[da_cobra]

Hi again,

I just added a new table to my sql database with a relationship of '1 to many' , but when I execute my application I get this error :

"System.Data.ConstraintException was unhandled
Message="Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints."

So now I have 2 tables :

tblCategories :
- IDCategory = relation 1 to
- CategoryName
- ...


tblMachines :
- IDMachine
- MachineName
- ...
- IDCategory many


(1 category per machine but many machines under a category, right?)

I know I didn't handled an exception, but why did this exception occured?

Since my English is not so very good, can someone explain what a constraint is? and why I get this error on this line :


tblCategoriesTableAdapter.Fill(machinepark_NVVetex_DataSet.tblCategories) ;


thx in advance