Hi,
It would be difficult to predict the issue with CN41N with the limited knowledge on the Objects this particular Project in questions have.
Also refer to http://service.sap.com/sap/support/notes/2003030
Here are the options that you can attempt:
1) Check the Project Structure. Do you have any other objects assigned to it like PM order, PP order etc.
2) If you have objects mentioned above, any master data can cause issues in CN41N.
3) Try to execute CNS41 as well as CN41 (Both has background option if the Foreground run exceeds the time limit set by the System)
4) Run CN41N by breaking the report execution for smaller data (Individual WBS Elements, networks etc), identify the Object thats giving issue.
5) Run CN41N with difference Data base profile (select/deselcting the multiple check marks)
6) Request ABAPer to start the trace on this transaction.
7) If Still unsatisfied with the results, please log an incident with SAP.
Hope that helps!
Thanks and Regards,
Varshal Kachole