You will only be able post a reopen purchase request if the associated Dimensions Accounts purchase order, is still in the batch, and can be edited.
To check if this is the case:
Log into FocalPoint website.
Find and select the purchase request in question.
Click Edit
Note down the the number in the Order No field.
Log into Dimensions Accounts
On the Purchasing tab, click the Orders icon.
Search for the purchase order you noted down in step 4.
Make the required edits directly to purchase order.
Click Save.