SYMPTOM:
Users may notice that after duplicating a project, in the new project it is impossible to create new metrics because of an error that occurs when validating the formula.
The error in Developer is:

Formula Incorrect

Validation failed with syntax error! Cannot find a function corresponding to + .Searching for + resulted in no matches
CAUSE:
This is an identified defect in Strategy 10.4 HF5 and 10.9.
ACTION:
This issue is fixed in Strategy 10.4 Hotfix 6 and 10.10. Please upgrade to take advantage of the fix.
WORKAROUND:
Restart the Intelligence Server or unload/reload the project.