Unable to Clear open item due to Exchange Rate Difference.

You need to define GL account for exchange rate differences, for example if you are posting an document with foreign currency converted into local currency at the time of payment and at the time of invoice posting there will be difference in exchange rates which will generate loss/gain from the transaction, for this you need to define GL accounts.

Financial acconting new----accounts receivable and accounts payables----business transactions------outgoing/incoming payments----outgoing/incoming payment global settings--define exchange rate different accounts, maintain accounts for exchange rate differences here, apart from if you are using foreign currency valuation program for valuation then define gl accounts in kdf transaction code and define exchange rate different key in kdb and assign that exchange rate different key in gl account for exchange rate different master records.