Retrieving the COM class factory for component with CLSID {XXXX} failed due to the following error: 80040154

In VS - project properties - in the Build tab - platform target =X86

I ran into a very similar issue.

I needed to use an old 32-bit DLL within a Web Application that was being developed on a 64-bit machine. I registered the 32-bit DLL into the windows\sysWOW64 folder using the version of regsrv32 in that folder.

Calls to the third party DLL worked from unit tests in Visual Studio but failed from the Web Application hosted in IIS on the same machine with the 80040154 error.

Changing the application pool to "Enable 32-Bit Applications" resolved the issue.

It sounds like your service was built against 'Any CPU', causing you errors on 64-bit where you are using COM components. You need to build it for x86.

The website is probably running as a 32-bit process which is why it can use the component. Building your solution against x86 will force your service to run as 32-bit.