Error : 69: invalid filelist specification

Please check the state of VSS and associated Writers

Have you done so? 

What do these commands show? 
vssadmin list writers
and 
vssadmin list providers

See :
How to verify Windows Open File Backup operation using VSSADMIN and BPFIS before contacting Symantec Technical Support
http://www.symantec.com/docs/TECH47808 

Please also tell us which OS on the client and NBU version and patch level.

Yes i have checked state of VSS and associated Writers and all is fine also looked at

https://support.symantec.com/en_US/article.TECH206217.html

the bigest data volume is 500GB

Error 69 on all backups?  Or just the backups from one policy?  If just one policy, check the "Policy type" in the backup policy front screen/header, is the "Policy type" still "MS-Windows" ?

vssadmin list writers shows a bunch of writers all stable and No error on last error

vssadmin list providers shows Microsoft software shadow copy provider 1.0 version 1.0.0.7

The error is for just one server in a policy all other servers in the policy are fine .

I have sheduled a reboot fo the server tonight before the daily backup is run

The server is running windows 2008 R2 and on NBU 7.6.0.4