Hi Alessandro,
Please use your web browser, and go to the quote server you're using to retrieve (FINRA ?). Once there, see if you can look up the quote for your bond. If you can find the bond price on the server, then record in Fund Manager's "Symbol" field whatever you had to use to look up the price. Usually this is the CUSIP. It needs to be entered in the symbol field, as that is what FM uses when requesting pricing data.
For links to all the available quote servers, please see:
http://www.fundmanagersoftware.com/intrtv.html