Code To Clear Data In A Column?

Using MS Access 2003 I am trying to build a command button in a form which clears the contents of a table column (which are tick boxes) - the idea behind it is this - the database is a contacts database for a club. Every year there is a subscription to be paid, so I want a column to annotate those who have paid (using a tick box). At the end of the year this will be reset - hence the reason for trying to produce a command button that clears out the ticks. What I using is this ....Private Sub Command11_Click()Dim strSQL As StringstrSQL = "UPDATE TBL-Master SET TBL-Master.campaign = '';"DoCmd.RunSQL strSQLEnd Sub(TBL-Master is the table name, campaign is the column name)What I am getting is a runtime error - 3144 -