Partially completed

Personally I would use Microsoft site to look for meaning and solution to WIN32 errors.

My interpretation of the errors:

(WIN32 3: The system cannot find the path specified. )
This says to me something on the system does not exist that is supposed to be there.
Either a typo error in the Backup Selection or a file/folder name got changed or deleted.

(WIN32 5: Access is denied. )
The Service Account used for NetBackup Client service does not have read permission.
Change Client Service logon account to a domain user with full access to all files/folders.
 

 (WIN32 32: The process cannot access the file because it is being used by another process. )
Exactly what it says. 
Check filename and find out from system owners why files are in use during backups.
Exclude them or ensure files are closed during backup window.
If this refers to live database files (e.g. SQL), exclude these files from MS-Windows policy and use proper agent to backup databases.