Database Software

I was trying to import dmp to a database from user1 to user1 using imp,but I got following errors.
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IMP-00017: following statement failed with ORACLE error 942
"ALTER TABLE "R_TASKSCHEDULE_SCHEDULE" ADD CONSTRAINT "F1R_TASKSCHEDULE_S" F"
"OREIGN KEY ("FK_TASKSCHEDULE_ID") REFERENCES "NC_TASKSCHEDULE" ("PK_TASKSCH"
"EDULE_ID") ENABLE NOVALIDATE"
table or view not exist
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so ,I export the indexfile of the DMP using imp test/pwd@cc file=xxx.dmp indexfile=xxx.txt log=imp.log rows=n
and see lots of table definition except tables with error notification such as R_TASKSCHEDULE_SCHEDULE

I got following questions:
1.why it's the first step to ALTER TABLE R_TASKSCHEDULE_SCHEDULE?instead of CREATE TABLE?
2.I can see lots of REM "create table" section,except the tables with error information

but the tables with error information did exist in the source database.but where are the DDL of error tables,there are only the ALTER TABLE in the indexfile

my environment source db:ora11.2.0.1+win2008, dest:ora11.2.0.1+linux
export by exp version 10.2.0.1
import by imp version 11.2.0.1

my exp and imp scripts
exp 123/pwd@cc file=xxx.dmp log=xxxx.log

imp 123/pwd@cc file=xxx fromuser=123 touser=123 log=xxx.log

-EOF-

thanks .....

Edited by: gunsnroses_xjapan on Jun 1, 2011 9:42 AM

Edited by: gunsnroses_xjapan on Jun 1, 2011 9:44 AM

Edited by: gunsnroses_xjapan on Jun 1, 2011 9:48 AM