My current store runs Joomla 1.5.26 and VM 1.1.19.
Installed Joomla 2.5.27 with VM 2.0.24d in a subdir. No demo data.
Had to use an older version of Virtuemart due to compability with our payment addon (updates are coming for this).
Purchased the excellent Virtuemart 2 Migrator but ran into some problems.
A couple of times during the VM migration i encountered errors.
See the attached image. I managed to get the migration past that point by unchecking "Users".
But i ran into the same problem when i came to "Orders".
vm_orders: Something went wrong... SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
Fatal error: Cannot access empty property in /[lots of directories]/administrator/components/com_vmmigrate/migrators/virtuemart.php on line 2591
[attachment cleanup by admin]
If you bought the Daycounts `migrator component from the VM extensions store then help is by ticket on http://extensions.virtuemart.net/ticket
If you bought from Daycounts website then support is by ticket on https://www.daycounts.com/support/new-ticket