What are the common Import / Export problems

ORA – 00001: Unique constraint (...) violated
You are importing duplicate rows.

Use IGNORE=NO to skip tables that already exist

(Imp will give an error if the object is re – created)

ORA – 01555: Snapshot too old 
Ask your users to STOP working while you are exporting or use parameter CONSISTENT=NO

ORA – 01562: Failed to extend rollback segment
Create bigger rollback segments or set parameter 
COMMIT = Y while importing

IMP – 00015: Statement failed ... object already exists...

Use IGNORE = Y import parameter to ignore these errors, but be careful as you might end up with duplicate rows