font recognized by fop processor

when i convert my xsl-fo to pdf with fop i receive this message

[INFO] building formatting object tree
[INFO] [1]
[ERROR] unknown font ,normal,normal so defaulted font to any
[ERROR] unknown font dialog,normal,normal so defaulted font to any
[ERROR] unknown font dialoginput,normal,normal so defaulted font to any
[ERROR] unknown font dialoginput,normal,normal so defaulted font to any
[ERROR] unknown font ARIAL,normal,normal so defaulted font to any
[ERROR] unknown font verdana,normal,normal so defaulted font to any
[ERROR] unknown font comics,normal,normal so defaulted font to any
[ERROR] unknown font ,normal,normal so defaulted font to any
[INFO] Parsing of document complete, stopping renderer

how can i solve the problem and is there a list of basic fonts supported 
by fop ?

regards, Emmanuel Garcia.