Thank you for your comment. I believe the question was bit confusing. Sorry about it.
Let me put this way ,
>> I use Netbackup 7.0 and Exchange 2010 RU3
>> I have edb file with committed logs – 20 to 50
>> I took FullBackup(#1)
>> It backed up edb file and logs – 20 to 50. After successful backup, it deleted 20 to 50
>> Then I had committed logs – 51 to 100
>> I took incremental backup(#2). It deleted 51 to 100 logs after successful backup.
>> Then I had committed logs – 101 – 200.
>> My logs file disk was running out of disk space.
>> So I deleted logs 101 to 150
>> Then I took incremental backup(#3) and it failed with event that log 101 missing (it was expected behavior)
>> I took full backup(#4) and it was successful and deleted the logs 151-200
>> I had committed logs – 201 to 300
>> I took incremental backup(#5), but it failed with event that log 101.
>> My expectation is, since I have taken fullback(#4) and it backed up EDB and log files – 151 to 200, the subsequent incremental backup should look for logs starting from 201, but in my case it failed with event that log 101 was missing.
>> Why it is so and how I can succeed with my future incremental backups. What should I do to succeed with incremental backup?