TF30063 error while updating NuGet packages

A customer started using the Ordina Team Foundation Server to host their project. Everything seemed to work fine. They can connect, check-in code and get the latest changes.However, they could not update NuGet packages! When running the command Update-Packagefrom the NuGet console, an error popped up: The Package Manager Console shows the same error, mentioning something about access denied errors....