The full error message reads:
Could not load file or assembly 'Microsoft.ReportViewer.WinForms, Version=126.96.36.199, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
This problem arises when you do not have the correct Microsoft ReportViewer software installed properly. Click here for information on getting the version of ReportViewer that your version of MainBoss needs.