Hi,
I believe your manifest file is not correct, because it's saying "Lab1PlaceGroup is not found"; as Bobby pointed out,you should specify full class name like this: <FullClassName>Lab1PlaceGroup.Lab1PlaceGroup</FullClassName>.
If you still get same issue, you can try to use addin manager tool to load your assembly, or use the addin manager tool to retrieve the manifest.
I believe your manifest file is not correct, because it's saying "Lab1PlaceGroup is not found"; as Bobby pointed out,you should specify full class name like this: <FullClassName>Lab1PlaceGroup.Lab1PlaceGroup</FullClassName>.
If you still get same issue, you can try to use addin manager tool to load your assembly, or use the addin manager tool to retrieve the manifest.