Sorry for the slow response Cynthia, it’s been a long week here.
Thanks so much for the icon and wallpaper, I really appreciate it! She is very cute 
The authentication seems to be working now, but based on the error code (which translates into ‘The specified module could not be found’), a piece of Messenger or Windows is missing. Out of curiosity, do any of your customization you’ve done include running any utilities that might have tried to make Windows smaller or otherwise remove parts of the operating system that might be considered obsolete or unused?
In the distant past, there were three parts of Windows/Messenger that tended to be missing that you could easily reinstall for this problem. There’s harm in trying them now, and to do so, download each link and run the MSI to install it. Each one will pop up an installer window, copy its files, and disappear when done.
Links: Error Reporting, C++ Runtime, and Communications Platform.
Then you can restart Messenger and try again.
Assuming that didn’t work, although it shouldn’t be necessary for Messenger to find its pieces, you can move that modified DLL back into the real Messenger folder and try running Messenger from the original location.
Assuming that still didn’t work, I might uncover more details now to get the connection log from Messenger itself. I have details on how to do that in a separate post:
Based on the results from that, we’ll have to see where to go from there.