Sudden failure on certain DFS shares

We use CIFS on our CentOS 6 systems to access numerous DFS shares hosted on a Windows 2008 cluster. Until yesterday this had proved to be very reliable.

Late yesterday afternoon we discovered that on two shares we could no longer create a directory or filename containing more than ten characters.

The length of the parent directory structure is 83 characters and we want to create a new sub directory with 50 characters which is well within the 255 limit permitted on Windows servers.

The relevant mount entry is:

//xxxxxx.com/PRDFS/OTRS_Index_CUST\134Index /opt/otrs/var/article cifs  rw,relatime,sec=ntlm,cache=loose,unc=\\xxxxxx \OTRS_CUST_Index,username=xxx,domain=xxx,uid=48,forceuid,gid=48,forcegid,addr=10.135.16.55,file_mode=0775,dir_mode=0775,nounix,prepath=\Index,rsize=61440,wsize=65536,actimeo=1 0 0

The exact error message is:

fs/cifs/dir.c: Full path: \Index\2016\08\26\check_permissions_5714_623122911_1472217688_224561 inode = 0x(null)
fs/cifs/inode.c: Getting info on \Index\2016\08\26\check_permissions_5714_623122911_1472217688_224561
fs/cifs/transport.c: For smb_command 50
fs/cifs/transport.c: Sending smb: smb_len=210
fs/cifs/connect.c: RFC1002 header 0x23
fs/cifs/connect.c: invalid transact2 word count
fs/cifs/transport.c: cifs_sync_mid_result: cmd=50 mid=36157 state=4
Status code returned 0xc0000034 NT_STATUS_OBJECT_NAME_NOT_FOUND
fs/cifs/netmisc.c: Mapping smb error code 2 to POSIX err -2
fs/cifs/cifssmb.c: Send error in QPathInfo = -2

All the parent directories exist.

Any advice really would be most welcome.

TIA

Shaun