Hi Satya
A purchase order is archived optically when the following required settings are available.
1. The purchase order output type has the storage Mode and Document type(MEOORDER) assigned (Tab : Storage system in output type settings). The relevant storage modes for optical archiving are 2 or 3.
2. Content repository is set up - Basis config ( Tcode: OAC0 )
3. The document type ( used in step 1 ) is assigned to a document class (Tcode: OAC2)
4. Linking object (For PO: BUS2012) and document type ( used in step 1) to content repository. (Tcode : OAC3)
I hope this info helps. Also please check if the below OSS note is relevant for your issue.
Note 591205 - Error while creating outgoing documents
Thanks
Ganapathy