Cause
You have placed a cable in the schematic to which you have assigned a part with fixed function templates (device). When placing the cable you have however used less functions (cable connections) than the corresponding part has. For example, you have selected a part for the placed cable that contains 4 cable connections of which you only use 3 in the schematic.
Solution
Possibility 1
Select a cable part with a suitable function template assignment (number of cable connections).
Possibility 2
Reduce function template settings for the selected part in the parts management (number of cable connections). To do this, select Utilities > Parts > Management, and in the Parts management dialog, select the Function templates tab. In the table, highlight the function templates you want to remove and click 
(delete). Copy the changed setting into the parts management. Then place the cable as a device in the schematic once again.
Then start a new check run.
Note:
Whether this message is issued depends on the Minimize unused functions and Number of unused functions settings. You move to the settings by firstly opening the Properties dialog of the device, bringing the Part tab to the front and clicking the [Device selection] button. In the Device selection dialog then click on [Settings] and open here the Settings: device selection dialog with the setting options previously stated above. Using the Number of unused functions setting you set the number of functions not used in the device (reserve functions) that the part should provide. The number can only be set if you have selected the Minimize unused functions check box setting.
If the Number of unused functions setting is set to "0", all unused templates will be identified as error(s) found.