Adding a suppression xml causes step to fail

Scan runs correctly and produces report.

However, when I add a suppression file the scan fails with the error below


Looking at the Logs I can see that there is a warning..

[WARN] Unable to create temp file for suppression file'D:\a\15\s\$\XXXX\DependencySuppression\DependencySupression20210630.xml'

Followed by:

[ERROR] Exception occurred initializing Vulnerability Suppression Analyzer.

YAML:

steps:
- task: dependency-check.dependencycheck.dependency-check-build-task.dependency-check-build-task@6
displayName: 'Dependency Check'
inputs:
projectName: 'XXXXMain'
scanPath: '$/XXXX/Main'
suppressionPath: '$/XXXX/DependencySuppression/DependencySupression20210630.xml'
warnOnCVSSViolation: true

XML file is under source control .