Subversion COPY/MOVE - File not found: transaction 'XXX-XX'

We had exactly the same issue and it is a pity that here are only useless answers.

This is not an svn problem, it is a nginx issue. As the OP mentioned in a comment, this has to do with whitespace (or other chars that needs url encoding) in the path. There happens an overencoding, so that the path is wrong, when it reaches svn.

Old open bug at nginx

But there is a workaround in the nginx rewrite rule, that avoids this additional wrong encoding:

Wrong encoding happens:

if ( $http_destination ~* ^(.*)$ )
{
    set $fixed_destination $1;
}

no additional encoding:

if ( $http_destination ~* ^(?<fix>.*)$ )
{
    set $fixed_destination $fix;
}    

The solution here is to use a named group, that is the difference that makes nginx behave differently in this case, but we did not found any documentation explaining this.

This unhelpful error message can occur if subdirectories on the destination path do not yet exist. Whilst you can manually create them (with svn mkdir) it is easier to use the --parents option.

    svn cp ^/trunk/bigproject ^/branches/experimental/bigproject -m 'test branch'

If branches or experimental did not exist then command would fail. This should work:

    svn cp --parents ^/trunk/bigproject ^/branches/experimental/bigproject -m 'test branch'

Probably your svn structure has no "Software/XXXXXX/branches" directory, it must exists in order to create "testbranch" here. You should make this directory ("branches") by hands and then do a branch.

I know that this is not the direct answer to your problems, but if you want to work with branches effectivly you should consider using other version control systems like git, mercurial or bazzar.

Or if you don't want to make the full migration, you can use git-svn was a "front-end" of your svn repository, i recommend you to read this to know more about git-svn.