The concrete problem has been resolved by an update. But here some background information regarding
tpm files and what one can do if one get the error
The .tmp file could not be parsed.
tpm-files contain information about a package: version number, included files, where they should be installed etc.
xml-files. And if they contain syntax errors then the parsing of the
xml can fail, like the "parsing" of a tex-file can fail. Here a faulty
& in a name was the problem.
tpm-files exist in two places: After the miktex installation there is a local copy of all existing
tpm in the main texmf tree in
tpm\packages. The package manager use this
tpm to show you e.g. the content of a package (right click ->properties).
These local files are updated when you synchronize.
If such a file is faulty after the synchronization you can open it with an
xml-editor and correct it. This should at least allow you to use the package manager (as long as you don't try to install the faulty package).
There are also online
tpm files. These are used by the update manager. They must be repaired by the miktex maintainer, so one should make a bug report like this https://sourceforge.net/p/miktex/bugs/2323/.