I ran across a weird error when I was trying to open an existing SSIS package in VS2005:

Error      1  Error loading 'Package.dtsx' : Unable to cast COM object of type 'Microsoft.SqlServer.Dts.Runtime.Wrapper.PackageNeutralClass' to interface type 'Microsoft.SqlServer.Dts.Runtime.Wrapper.IDTSContainer90'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{8BDFE892-E9D8-4D23-9739-DA807BCDC2AC}' failed due to the following error: Library not registered. (Exception from HRESULT: 0x8002801D (TYPE_E_LIBNOTREGISTERED))

To fix the problem do the following:

1.       Open the command prompt

2.       Navigate to C:\Program Files\Microsoft SQL Server\90\DTS\Binn

3.       Run C:\Program Files\Microsoft SQL Server\90\DTS\Binn>regsvr32 dts.dll

That should fix the problem.