This issue exists as of Penelope 4.23.1.0
What happens?
An error is thrown when trying to book an event in Implementation, stating ERROR: invalid input syntax for integer: ""
Workaround?
Go to SA → MSExchange
Click Edit
Check 'Enable MsExchangeSync'
Choose one of Transports and enter some fake credentials
Click Save
Click Edit
Disable MsExchange Sync and Click Save