cannot make connection between letter and database

For the pupose of a mailmerge I try to make the connection (VIEW → DATASOURCES) to a database from the letter, but I get this message:
“The connection to the datasource “xxxxx” could not be established”
“The file “xxxx” could not be loaded”


Please be kind enough to provide some minimal information:

Is this something which was working before? Is this regarding Writer? LO version? OS? What database are you using? If it is HSQLDB embedded is proper Java installed and enabled?