Solution : https://service.sap.com/sap/support/notes/143524 (SAP Service marketplace login required)
Key words : 
system performs full table scans, project information system, additional key words, exec sql statements, tables m_prpoa, networks exist, solution release 4, source code, optimizer hints, prerequisites
Related Notes : 
       
| 401949 | Long validity periods in PS reporting III | 
| 339596 | TIME OUT whn insertng WBS in prjct (ORACLE problem) | 
| 313466 | LDB PSJ: Dump with "INTERNAL ERROR LDB PSJ" III or ok020 | 
| 200228 | Performance problems in PS under Oracle | 
| 182652 | Long Runtimes in PS Reporting II | 
| 180911 | Problem in ORACLE with initial values | 
| 161537 | LDB PSJ: Performance with Oracle database | 
| 146444 | GET_PS_OBJECTNUMBER: Long runtime II | 
| 135254 | Perfrmance problems in Projct System as of Rel. 4.0 |