Symptoms

The errors appear in Event log of Office365 backup set, i.e:

>> 9/20/19 10:05:30 AM    admin    Application    0xC0000013    9841        Directory path is too long.  (\\GRAPH.MICROSOFT.COM\VirtualShare:Office 365 Groups

>> 9/20/19 10:03:56 AM    admin    Application    0xC0000390    9841        Invalid buffer size: 0 bytes.


as a result, the backup set crashes with the message:

>> 9/20/19 11:29:20 AM    admin    Exception    0xFFFFFFFF    9841        Read access violation exception at 7ff886c5caa7 (rip=7ff886c5caa7, rax=1c7fc0c7e0c,xmm0=2caacfc130, rbx=00020000,rcx=000074e0,rdx=fffffffffc6fe6d4, rsi=1c7f87df000,rdi=1c7fc0e092c,rsp=2caacff9b8,rbp=00000000)
 00007FF886C5CAA7 (VCRUNTIME140): (filename n, class:CException exception (FileReadWorker.cpp,line 60)

Cause

The backup source directory path name is too long. The path length should not be longer then 800 characters.(in Windows DS-Client v14.1 HF6, and before).


The foldar length includes: the web domain name + the directory / document name + additional 37 characters for the each directory / document ID#,

i.e. "(01BZGRJHHIQZBAAYCWS5C36WQR45VXHQPD)"

Workaround

Reduce the backup source directories/documents path name less than 800 characters in total.