Failed to stat file, migrating kvstore v8.2

[Snorre]

I'm trying to migrate kvstore on a v8.2 installation on Windows, but it fails early in the process.

splunk migrate kvstore-storage-engine --target-engine wiredTiger

ERROR: Cannot get the size of the KVStore folder at=E:\Splunk\Indexes\kvstore\mongo,
due to reason=3 errors occurred. Description for first 3: [{operation:"failed to stat file",
 error:"Access is denied.", file:"E:\Splunk\Indexes\kvstore\mongo"},
 {operation:"failed to stat file", error:"Access is denied.", 
file:"E:\Splunk\Indexes\kvstore\mongo"}, {operation:"failed to stat file", 
error:"Access is denied.", file:"E:\Splunk\Indexes\kvstore\mongo"}] 

 I've tried to do file operations on the folder and subfolders of E:\spunk\indexes\kvstore\mongo and everything seems ok.

The mongod.log does not contain any rows from the migration.

Any nudges in the right direction? Can I upgrade to 9.1 without migrating the store?

[Snorre · Accepted solution]

I started using Process Monitor from SysInternals to see what files the migration tool had problems with and when I fixed permissions on those the problem was fixed.