When attempting to create a new Team Project in TFS 2015 R2 (on-Prem) with a custom Process Template, I received this error popup:
This was a surprise, because our customized process template is based off of the default Microsoft Scrum template.
Almost nobody else had this error on the internet from my google-fu. I believe I have a solution and will answer this question accordingly if so.
If your Scrum template was from before the introduction of Git in Team Foundation Server you'll likely need to edit your VersionControl.xml to include the Git references there:
<?xml version="1.0" encoding="utf-8"?>
<tasks>
<task id="VersionControlTask" name="Create Version Control area" plugin="Microsoft.ProjectCreationWizard.VersionControl" completionMessage="Version control Task completed.">
<taskXml>
...
<git>
<permission allow="GenericRead, GenericContribute, ForcePush, Administer, CreateBranch, CreateTag, ManageNote" identity="[$$PROJECTNAME$$]\$$PROJECTADMINGROUP$$" />
<permission allow="GenericRead, GenericContribute, CreateBranch, CreateTag, ManageNote" identity="[$$PROJECTNAME$$]\Contributors" />
<permission allow="GenericRead, GenericContribute, CreateBranch, CreateTag, ManageNote" identity="[$$PROJECTNAME$$]\Build Administrators" />
<permission allow="GenericRead" identity="[$$PROJECTNAME$$]\Readers" />
</git>
</taskXml>
</task>
</tasks>
Adding that blob to the file should allow you to complete the process.