I came across an interesting error today when building an Advanced Find view on Service Activities with data fields added from the related Opportunity. I received a generic error message when I ran the query so I turned Dev Errors on and ran the Advanced Find query again. With Dev Errors on, I received a nice long error message that included, "transactionCurrencyId needs to be supplied to format a transaction money field".
I Binged the error message and found the answer. It appears that you need to add the TransactioncurrencyID field of the related entity if you add currency fields from the related entity. I added the currency field from the Opportunity and the Advanced Find query ran like a dream.