Deactivate is grayed out because there is a blank value in the account field. The blank (Null) account could not be deleted. Therefore deactivate is not available as an option.
Salesforce Securlet. Any environment.
The null account is not valid so it will not allow for deactivation.
Go to the deactivate page, hit purge, and then rename the null account to a named account. It should now be possible to deactivate. Securlet can now be reactivated with a new account.