(Not sure if this is the same for Capital Req but we have had a very similar error message.)
When Finance sets up a new dept account code, that code will work in PO20 with no problems. But, if you want to issue items (IC21) or use req center, that department needs to be activated in RQ01. (I'm not sure how Captial works in Req center.)
ALSO (this is key) the expense accounts need to be activated for that department in GL20. I do not have access to GL20, so I send a list of what expense accounts I want activated for that department. (There is no need for Administration to use the expense code INSTRUMENTS for their department.)
*There is also sub accounts that some places use. We mostly have 0 and 1001 (general). Finance "turned off" the 0 accounts but it shut them all off. We just know to choose/add 1001 as the sub account.
Hope this helps at least one person! LOL