How can i send an error message at EXIT_SAPMM06E_013 ?

Question

Hi
I'm making some validations to Vendor and Partner Functions (table control in 'Partners' Strip) in Creting/Changing Purchase Orders (ME21N/ME22N). 
I know the suitable user exit is EXIT_SAPMM06E_012 for making validation before saving, but this exit does not has (receive) the table with Partner Functions so i could validate them.
Then I use the Exit _013, wich executes when saving the PO, because this exit has the captured Partners table (XEKPA).
But, when i make the validations and try to send a error mesage,  the system shows other message type info (window) like 'The requested object is locked by another transaction' and then another like 'System error (error in method PO_POST)'.
I think this it's because the exit _013 is better suitable to make customer updates and not validations, that it's because just passing by MESSAGE Ennn(cc) command makes the methods catch my error and send other errors and close the transaction.
Does somebody can help me ??
How can i send error messages in exit _013 ??
Or is this incorrect ??
Or in wich User Exit can i validate the Partner Functions ??
I really will aprettiate if somebody can help me, because i'm delayed with my development !!
Regards

Answer 1

Hi Frank,
The eror message you are getting seems to be coming from somewgere else and may be due to the same PO being cahnged in another transaction or have you put some code in BADI ME_PROCESS_PO ( Method POST) .
You can try by commenting out the code in EXIT 13 .
If this does not work then use EXIT 12 only and below is the code you can use to access XEKPA in exit 12.
DATA IT_EKPA LIKE EKPA OCCURS 0 WITH HEADER LINE.
DATA NAME(50) VALUE '(SAPLMEPO)XEKPA[]'.
DATA NAME1(50) VALUE '(SAPMM06E)XEKPA[]'.
FIELD-SYMBOLS <F1> TYPE ANY .
IF SY-TCODE+4(1) = 'N'.
ASSIGN (NAME) TO <F1>.
ELSE.
ASSIGN (NAME1) TO <F1>.
ENDIF.
IT_EKPA[] = <F1>.
( Now you have the data in IT_EKPA table which you can use to validate )
Cheers