If SQL Server 2005 Express (RE_Express or FE_Express) fails to install, then review for applicability Knowledgebase Solution BB602180 regarding a known Microsoft issue.

If receiving the error in The Raiser's Edge: 
    Update/repair the RE_Express instance on the server

    If receiving the error in The Financial Edge, The Education Edge, or the above steps did not correct the error in The Raiser's Edge:

      Update/Repair the Blackbaud Management Console on the server