Oracle Database Discussions

Hello everyone,
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit Production

I've two tables PART_TEMP1 (day wise PARTITIONED BY RANGE ON COL2) & NOPART_TEMP2 (NON-PARTITIONED)

TABLE STRUCTURE IS SAME FOR BOTH
Name Null? Type
----------------------- -------- --------------------------
COL1 VARCHAR2(10)
COL2 DATE

When I exchanged partitions with below statement it was successful.
ALTER TABLE PART_TEMP1 EXCHANGE PARTITION APR14 WITH NONPART_TEMP2;

But now I want to exchange (from part_temp1 to nonpart_temp2 table) APR15 partition
ALTER TABLE PART_TEMP1 EXCHANGE PARTITION APR15 WITH NONPART_TEMP2;
Then I get below error
ORA-14099: all rows in table do not qualify for specified partition

All I want to do is move data from PART_TEMP1 TO NONPART_TEMP2. But second time, it seems that it's doing vice-versa

I want to know where I'm going wrong.

thanks