When your round uses submission tracks, each track's submissions are scored with the evaluation form assigned to that track. If a track isn't assigned to any evaluation form, there's no scorecard for its submissions, so evaluators can't evaluate them.
Why it matters
Each evaluation form is linked to one or more submission tracks.
A submission can only be scored with a form that's assigned to its track.
If you add a new track later, it isn't linked to an evaluation form until you assign it.
If your round doesn't use tracks, there's one evaluation form for the whole round and you don't need to assign anything.
The symptom: evaluators can evaluate some submissions but not others
Your evaluation dates are open and the evaluator can see their assigned submissions, but the Evaluate button is greyed out or missing for some of them. Usually those submissions are all in the same track. That track is very likely not assigned to an evaluation form.
Check which tracks a form covers
Open your program and click the round's tab.
Click the Evaluation Form tab.
In the form selector, choose an evaluation form. It shows as "Form name ( Linked to Submission Form(s) )".
Click the Edit icon (pencil) next to the selector. The Edit Evaluation Form dialog opens.
Look at Assign to submission track (Category). It lists the tracks this form scores.
Repeat for each evaluation form in the round. Every track that receives submissions should appear in a form's list.
Assign a track to an existing evaluation form
In the round's Evaluation Form tab, choose the form in the selector.
Click the Edit icon (pencil).
Open Assign to submission track (Category) and select the missing track. You can select several tracks.
Click Save.
Create a separate evaluation form for a track
Use this when a track needs its own criteria.
In the round's Evaluation Form tab, click the Add Form icon next to the form selector.
Enter a Form Title.
Under Assign to submission track (Category), select the track or tracks.
Optional: use Clone fields from another form to start from an existing form.
Click Save, then build the questions. See Building Your Evaluation Form.
Fix it step by step
Confirm the round's Evaluation Dates are open (round Settings → General Settings).
In the round's Submissions tab, check the Track column of the submissions that can't be evaluated.
In the Evaluation Form tab, make sure that track is selected in a form's Assign to submission track (Category). If not, add it and click Save.
Ask the evaluator to reload their page and try again.
Tips
One evaluation form can cover several tracks, or each track can have its own form.
Different forms can have different maximum scores, so totals across tracks may not compare directly.
The Assigned Track column in the round's Evaluators tab shows which track each evaluator is assigned to.
Whenever you add a new track, assign it to an evaluation form straight away.
Still stuck? See Troubleshooting: Evaluators Can't See or Evaluate Submissions.