The roll is being used at the moment due to several reasons:

1) recording to this roll is in progress;

2) another user is working with this roll or it's descendants. To check who locks the node go to Cinegy Archive Manager => Nodes Explorer;

3) some objects in the database (e.g. ClipBins, sequences) refer to the descendants of this roll. Right-click the roll in CMD explorer window and go to Media Cleaner, it will show all the objects that use the descendants of this roll.