Until now, the Put on leave module allowed to enter any type of absence for a collaborator without any control.
From February 15th, 2016, you cannot enter anymore an absence for a collaborator on an account of which the balance will be negative at the end of the month if the parameter "What happens in case of a debit balance?" has for value "Request block" (Parameters > Accounts).
Sick days specificity
If your configuration prevents you from entering "Sick days", as it creates a debit, you have to check the account parameters in the module: Parameters > Accounts.
For example, you cannot enter a sick leave if the parameters are the following ones:
In order to put on leave on such type of accounts, you'll have to authorize the debit.