You don't need to shout, especially not if you are not looking at the place where SAP is checking.
Plant existence is checked against table T001W,
If someone deleted a plant for what ever reason (without thinking) in a sandbox system, then the plant is gone but still you find entries like POs or material masters having this plant referenced.
Further you should post the original message instead of rephrasing a message, SAP has multiple 10000 messages, some are quite similar, so it is usually very important to post the correct content of a message, even better to post it together with a message number.
Not to forget that you always should try if you can do the same thing in the online transaction ME22N, a BAPI cannot do wonders if the normal transaction doesn't allow.