Exchange database backup fails

Exchange database backup fails with this error..

Can anyone advice what "Driver not active for volume" means? There's literally zero reference about it on the internet.

Many thanks !

107092:nsrnmmsv: Version information for C:\Program Files\EMC NetWorker\nsr\bin\nsrnmmsv.exe: Original file name: nsrnmmsv.exe Version: 9.1.0 (ntx64) Comments: Supporting Microsoft Volume Shadow Copy Service

127159:nsrnmmsv: Created temp path C:\Program Files\EMC NetWorker\nsr\tmp\nmm\2018-09-07_11-41-02_5492-5496\.

nsrnmmsv: multithreaded save set parallelism==6

145369:nsrnmmsv: Initialization success -- Exchange shell successfully initialized. Required for Exchange.

133296 1536334864 0 0 0 5496 5492 0 client-computer.domain.com nsrnmmsv NSR info 26 Starting backup operation. 0

145369 1536334865 0 0 0 5496 5492 0 client-computer.domain.com nsrnmmsv NSR info 89 Initialization success -- Exchange shell successfully initialized. Required for Exchange. 0

159219 1536334867 5 0 0 5496 5492 0 client-computer.domain.com nsrnmmsv NSR critical 31 Driver not active for volume %s 1 0 48 \\?\Volume{e200533e-0a8b-11e8-9b19-000c29e7b1bf}

95958 1536334867 5 0 0 5496 5492 0 client-computer.domain.com nsrnmmsv NSR critical 36 Cannot initialize the write tracker. 0

95959 1536334867 0 0 0 5496 5492 0 client-computer.domain.com nsrnmmsv NSR info 87 The write tracker initialization failed. Performing a block based backup at level full. 0

137907 1536334867 2 0 0 5496 5492 0 client-computer.domain.com nsrnmmsv NSR warning 66 Unable to start write tracker session. Backup cannot be completed. 0

139527 1536334867 3 0 0 5496 5492 0 client-computer.domain.com nsrnmmsv NSR error 51 The backup operation did not complete successfully. 0

102333 1536334867 3 0 0 5496 5492 0 client-computer.domain.com nsrnmmsv NSR error 21 Exiting with failure. 0

2018-09-07 3:41:07 PM Removing files under temp path C:\Program Files\EMC NetWorker\nsr\tmp\nmm\2018-09-07_11-41-02_5492-5496.

--- Job Indications ---

Internal error. Save job failed, please refer to log file for more information.

client-computer.domain.com:pseudo_saveset: retried 1 times.