SAP Note 23974 - ME56, ME57: Cancellat. in popup 'Manual Allocation'

Symptom:

Transaction ME56/ME57
If several list entries are selected and you allocate a source of supply manually, you cannot cancel the entire transaction in the popup using the 'Cancel' function but you can only skip the current entry.

Cause and prerequisites

The required function of the immediate 'Exit' is currently not supported.

Solution
'Temporary workaround':
Enter, for example, a nonexisting vendor and press the 'Cancel' key after the error message.