On *nix machines oracle provides the command line oerr utility. It can be very handy. Usage is simple, just give it your error code and it gives you (somewhat) more info:

$ oerr ora 12450
12450, 00000, "LOB datatype disabled in LBAC initialization file"
// *Cause:  You tried to specify a LOB datatype for a column or attribute,
//          but the use of the LOB datatype has been disabled.
// *Action: Change the LBAC initialization file to allow the creation
//          of LOB columns and attributes.