Problem in modifying the table data through sm30 change button

In my table i have 5 fields startdate(key),enddate(key),fromyear(key),toyear(key),value

                requirement is between these,i.e 01.01.1997 to 31.12.1998 if the employee serviced from 1 to 2 year some amount we need to maintain some in value field.

Here whenever the user choose new entry iam validating the dates overlapping in 05 event and whenever the user copying an existing record also iam validating the copied record in 21 event of TMG.

Now the problem is when we go to sm30 and click on change button and modified the only amount in value field and press enter at this time also the Dates overlapping is condition is triggered which we have written previous.

                   Could u please anyone help me in resolving this is greatly appreciated..thanks in advance.

regards,

kranthi