When the user receives their SoftToken activation email, the "Activation PIN" field is blank.
There is an issue with the way that the Activation PIN is stored in the database
Unassign the SoftToken that is having the issue from the user
v3.x Remove the SoftToken from the database using the "Delete Unassigned Tokens" screen of the AuthAnvil Configuration Wizard.
v4.x-newer Remove the SoftTokens from the Tokens Tab in the AA Manager
Then, re-add the SoftToken using the original token import file. You should now be able to assign this SoftToken to a user.
AuthAnvil 3.x - newer