Recently I met a case in which customer met zero net value in VF01 after EHP 6.6 upgrade.
Their scenario is SO - PR - PO - STO delivery - stock transfer invoice.
After further analysis, it leads to one condition type which has calculation formula RV64A901. This formula used to be working in their non-upgrade system but leads to 'inactive' for this condition type after upgrade. ( see below )
So I set breakpoint for formula RV64A901 and restart VF01.
It stopped in RV64A901 as expected then I set watchpoint for SY-SUBRC. Then F8 to trace the change of SY-SUBRC.
SY-SUBRC changed to 4 after the selection below.
The selection failed due to the empty fields KOMP-AUBEL and KOMP-AUPOS. (see above)
Then WHY the two fields are cleared? Any note correction caused for it? Thinking into this direction and found note 321099 may be interesting here.
The effect of the note 321099 correction is that the fields AUBEL and AUPOS of the commnuication structure KOMP are cleared if an intercompany billing for stock transfer order is created. (see below)
To solve it, customer should implement user-exit USEREXIT_PRICING_PREPARE_TKOMP (RV60AFZZ) to re-populate the fields TKOMP-AUBEL and TKOMP-AUPOS.
This user-exit will be called in the end of form PREISFINDUNG_VORBEREITEN.
Now problem solved.
Hope it gives you some hint in some way.