we are using 8i server

RMAN> run {allocate channel c1 type disk format 'd:\oracle\backup';
2> backup database;}

RMAN-03022: compiling command: allocate
RMAN-03026: error recovery releasing channel resources
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure during compilation of command
RMAN-03013: command type: allocate
RMAN-06172: not connected to recovery catalog database

It is very confusing for me why i am facing this error?
can anybody help me in this regard?