Diagnosis
In the Implementation Guide (IMG) you chose the Customizing settingthat stipulates that currency changeover takes place after an accountbalancing.
Since the balancing prior to the changeover date falls on a non-workingday, the account is blocked for this balancing. (This applies if thebalancing posting date is later than the balancing date when thebalancing is executed). This means you must first carry out thecurrency change before the balancing. This leads to the postingsresulting from the balancing being made in EURO.

Procedure
If this is not what you want, first choose another date for thecurrency changeover or adjust the balancing time periods (key date ornext date) accordingly.