CWD Command Fails

I'm using the .Net library PutFile() method to upload a file. Getting the following error:

Ascii transfer mode selected.
. 2017-03-30 15:51:07.025 Starting upload of \\Canton\data\Real Estate\ims\FTP TRANSFERS\bankfile.txt
> 2017-03-30 15:51:07.025 CWD /'FTSTRS02.'/FTSTRS02/
< 2017-03-30 15:51:07.181 500 User Exit denies Userid 'FTSTRS02' from using Command 'CWD'.
> 2017-03-30 15:51:07.181 CWD /'FTSTRS02.'/
< 2017-03-30 15:51:07.290 500 User Exit denies Userid 'FTSTRS02' from using Command 'CWD'.
> 2017-03-30 15:51:07.290 CWD /
< 2017-03-30 15:51:07.399 500 User Exit denies Userid 'FTSTRS02' from using Command 'CWD'.
. 2017-03-30 15:51:07.399 Copying files to remote side failed.
* 2017-03-30 15:51:07.399 (ExtException) **Copying files to remote side failed.**
* 2017-03-30 15:51:07.399 User Exit denies Userid 'FTSTRS02' from using Command 'CWD'.

What is the CWD command trying to do? It appears to be issued by WINSCP 3 times here.

WINSCP Version: 5.5.5, Windows 7 Enterprise

WinSCP may not be compatible without your server.

But in any case, you should try to the latest version of WinSCP first. There have been some relevant improvements.