I recently ran into a problem with a client's SQL 2005 Standard server where the Express Edition of SSMS (Management Studio) had been installed.  The Express Edition had to be completely removed and the Standard version of SSMS was installed.

However, I kept seeing the following error when I tried to open my Maintenance Plans...
<p style="padding-left: 30px"><em>Method not found: 'Void Microsoft.SqlServer.Management.DatabaseMaintenance.TaskUIUtils..ctor()'. (Microsoft.SqlServer.MaintenancePlanTasksUI)</em></p>
The problem was that SSMS was at a different patch level after I re-installed it.  I installed SP4, which was the patch level of the Database Engine, and everything worked!

<strong>Please note:</strong> The first time you open the Maintenance Plan after patching you will see the following error, which can be ignored...
<div style="padding-left: 30px"><em>The DDS Layout contains an invalid control progid. The layout will be regenerated.</em></div>
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