V6 Dynamic File Folder Upload - " Destination Directory not available"

I want to save files to folders based on the User Id. In this case the UserId is 649

In a custom code block after Submit I have:

<?php $this->set("mypath", "G:\wamp\www\GoldRibbon\components\com_chronoforms6\chronoforms\uploads\Cust{user:id}");
?>

Using custom code block {var.pr:mypath} this prints out correctly as:

G:\wamp\www\GoldRibbon\components\com_chronoforms6\chronoforms\uploads\Cust649

The Upload Directory Path is set to : {var:mypath}

On an upload I get the error message "Destination directory not available." The folder definitely exists on my computer.
​

The debugger results are:

Array
(
[option] => com_chronoforms6
[chronoform] => test-copy
[event] => submit
[user_id] =>
[radio8] => n
[file19] => Jennifer A side1.pdf
[aid] => 25
[text1] => don is here
[button2] =>
[Itemid] =>
)
Array
(
[save_data10] => Array
(
[data] => Array
(
[option] => com_chronoforms6
[chronoform] => test-copy
[event] => submit
[user_id] => 649
[radio8] => n
[file19] => Jennifer A side1.pdf
[aid] => 25
[text1] => don is here
[button2] =>
[Itemid] =>
[modified] => 2018-05-06 23:06:56
)

[_success] => Data saved successfully
[log] => Array
(
[0] => UPDATE `chronoforms_data_test` AS `data8` SET `user_id` = '649', `radio8` = 'n', `file19` = 'Jennifer A side1.pdf', `text1` = 'don is here', `modified` = '2018-05-06 23:06:56' WHERE `aid` = '25';
)

[var] => Array
(
[user_id] => 649
[radio8] => n
[file19] => Jennifer A side1.pdf
[text1] => don is here
[modified] => 2018-05-06 23:06:56
)

)

[upload15] => Array
(
[path] => G:\wamp\www\GoldRibbon\components\com_chronoforms6\chronoforms\uploads\Cust649\
[var] =>
)

)
}

Hi drgolden ,
​
Is the folder writeable by the Joomla! user?
​
Bob

The folder is writeable. If I just input the path without using the {user:id} variable it works fine.
​
In custom code this php statement gets me to the uploads directory
​
<?php
$this->set("mypath1", $path.DS."components".DS."com_chronoforms6".DS."chronoforms".DS."uploads".DS);
?>
​
I think my problem is with syntax. What would be the proper syntax to add "cust" + the {user_id} variable to the end of this statement so the path ends with (assuming the user_id is 649)?:
​
.../chronoforms/uploads/cust649