Failed to load data access DLL

2013-06-03 10:55:33 +0000

While attempting to debug a crash dump from a .NET 4.0 RTM process on my (.NET 4.5), I got the dreaded Failed to load data access DLL, 0x80004005 error message.

tl;dr? Skip to the end…

In full, the error looks like this:

0:000> .loadby sos clr
0:000> !vmstat
Failed to load data access DLL, 0x80004005
Verify that 1) you have a recent build of the debugger (6.2.14 or newer)
            2) the file mscordacwks.dll that matches your version of clr.dll is 
                in the version directory or on the symbol path
            3) or, if you are debugging a dump file, verify that the file 
                mscordacwks_<arch>_<arch>_<version>.dll is on your symbol path.
            4) you are debugging on supported cross platform architecture as 
                the dump file. For example, an ARM dump file must be debugged
                on an X86 or an ARM machine; an AMD64 dump file must be
                debugged on an AMD64 machine.

You can also run the debugger command .cordll to control the debugger's
load of mscordacwks.dll.  .cordll -ve -u -l will do a verbose reload.
If that succeeds, the SOS command should work on retry.

If you are debugging a minidump, you need to make sure that your executable
path is pointing to clr.dll as well.

There are lots of words here, but they’re not the easiest to understand, particularly when you’re in a hurry (like, say, you’re attempting to debug an issue on a production server).

I’m assuming that you’ve got a recent version of WinDbg. I was running 6.12, which should be OK.

If you’re lucky, however, (and you’ll need to have !sym noisy turned on to see this), you’ll get:

DBGHELP: clr - public symbols  
         c:\websymbols\clr.pdb\0A821B8A573E42899202851DF6A539F12\clr.pdb
SYMSRV:  mscordacwks_AMD64_AMD64_4.0.30319.01.dll from http://msdl.microsoft.com/download/symbols: 502605 bytes - copied         
DBGHELP: c:\websymbols\mscordacwks_AMD64_AMD64_4.0.30319.01.dll\4BA21EEB965000\mscordacwks_AMD64_AMD64_4.0.30319.01.dll - OK

This means that the Microsoft Symbol Server had the relevant mscordacwks.dll file. If not, you’ll have to copy it from the machine from where the crash dump originates, and put it somewhere useful. Unfortunately, the message doesn’t explain what, exactly, it means by “on your symbol path”.

For me, at least, it seems that putting it in (e.g.) C:\WebSymbols doesn’t work – you need to put it in the correct named location. I can’t verify this right now, since it downloaded it successfully from Microsoft Symbol Server.

More importantly for my problem, however, is the easily-overlooked message at the end:

If you are debugging a minidump, you need to make sure that your executable
path is pointing to clr.dll as well.

Given that WinDbg knows that I’m debugging a minidump, it could have made this more prominent. What it’s telling us is this:

  1. Copy clr.dll from the original machine. Put it somewhere. Next to the dump file would be fine.
  2. Add that path to the executable search path, using .exepath+ C:\wherever

Note, that you must use the version from the original machine. If you attempt to use your clr.dll, you’ll get the message:

The version of SOS does not match the version of CLR you are debugging.  Please
load the matching version of SOS for the version of CLR you are debugging.
CLR Version: 4.0.30319.1
SOS Version: 4.0.30319.17929
CLRDLL: C:\Windows\Microsoft.NET\Framework64\v4.0.30319\mscordacwks.dll:4.0.30319.17929 f:8
doesn't match desired version 4.0.30319.01 f:8

Just tell me what to do, already!

  1. Copy clr.dll, sos.dll and mscordacwks.dll from the machine where the crash is occurring.
  2. Put them in C:\Temp.
  3. .exepath+ C:\Temp
  4. .load C:\Temp\sos
  5. Done, you can now !vmstat, etc., to your heart’s content.