when synchronizing offline and online databases

while synchronizing online and offline databases i get this error,

Run-time error'-2147217873 (80040e2f)':

Violation of PRIMARY KEY constraint 'PK_Item'. Cannot insert duplicate key in object 'dbo.Item'.

I have dropped the offline database several times and still get the same error, i guess the error is in my primary database. what could be the safest solution to this problem.

thank you all in advance