We recently ran into an issue in SalesLogix version 7.5 sp3 where the mail merge did not work after an install. Clicking on the write->email menu would bring up the following message:
 
The Following HTTP status error was reported in THTTPRequestThread.Execute: Retrieving the COM class factory for component with CLSID{1BBD3B34-C697-449A-AE6B-37A18D338C0F} failed due to the following error: 80040154
 
The issue was traced back to the mail merge dlls not being registered on the server even though the installation process seemingly went through successfully.
 
To resolve this, un-register and re-register the following DLLs
SLXMMGUI.dll SLXMMEngine.dll SLXMM.dll
 
If these files are missing, then you will need to find them from a working installation and just copy them over and register them.
 
Sometimes this issue also occurs if the following registry key is missing:
HKEY_CLASSES_ROOTCLSID{1BBD3B34-C697-449A-AE6B-37A18D338C0F}
 
You will need to export this registry key from a working installation and re-import it to the affected server.
 
Finally rebuild and redeploy the SalesLogix website to republish all changes to the website.