Solution : https://service.sap.com/sap/support/notes/715484 (SAP Service marketplace login required)
Key words : 
people centric - user interface, individual billable business transactions, http 500  internal server error, internal error reading, billing due list, 'individual billing', error occurred, program error, results list, 'collective billing'
Related Notes : 
       
| 710710 | |
| 709921 | CRM 4.0 SP Stack 4/2004 (SAPKU40005): Release & Info. Note |