blocking the transaction to release manually the Purchase Requisition

[Felipe Uribe - SAP]

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Hi Everybody,
 
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I have developed a WF to release the Purchase Requisition, nothing =
special but I have a doubts about the permissions to access the =
transaction to release the document manually ME54, I mean, The User =
which is gonna approve the document will have to make it using Workflow =
and Workflow uses the transaction ME54, same transaction to release it =
manually.
 
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Te question is how could I block this transaction to avoid the user to =
use it manually but I can't block it because Workflow is gonna call this =
transaction in the method.
 
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There is any possibility using the authorizations or something in the =
profile??
 
 ....Idem with Purchase Order
 
Thanks a lot.
 
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