Conversion failed when converting the nvarchar value

The code below cause an error Conversion failed when converting the nvarchar value '6, 24' to data type int.  The AlertStatuschange is set as *6*, *24* thus I remove the * to match the number but keep getting the error.

SELECT  tlbAlertchange.ShipmentID, customer_employees.EmployeeLast_Name,  customer_employees.EmployeeFirst_Name,  
        customer_employees.EmployeeEmail_Address,  customer_employees.EmployeeFax_Number,
      customer.Fax_Number,  tblactevents.ActivityID, customer_employees.AlertStatuschange
 FROM  tlbAlertchange  
      INNER JOIN tblactevents ON (tlbAlertchange.acteventsID = tblactevents.ActEvetID)
      INNER JOIN tblshipment ON (tlbAlertchange.ShipmentID = tblshipment.ShipmentID),  customer  
      INNER JOIN customer_employees ON (customer.CustomerID = customer_employees.CompanyID)
WHERE  (tblshipment.CLIENT_ID = customer_employees.CompanyID) and tblactevents.ActivityID in (replace(customer_employees.AlertStatuschange,'*',''))
Group by  customer_employees.EmployeeLast_Name,  customer_employees.EmployeeFirst_Name,
       tlbAlertchange.ShipmentID,  customer_employees.EmployeeEmail_Address,
       customer_employees.EmployeeFax_Number,  customer.Fax_Number,
customer_employees.AlertStatuschange,tblactevents.ActivityIDStart Free Trial