The flow OverrideStagingTableValues has an authentication block which makes reference to VTDM_user and VTDM_password as such:
" & VTDM_user & " " & VTDM_password & "

Our password variable is encrypted (and has been for a long period of time) but a recent upgrade in Javelin versions seems to fail to decrypt this as we are suddenly getting an authentication error on this step. If we hardcode our password into VTDM_password (instead of the encryption), it authenticates appropriately.

I tried with the latest Javelin 2.0.501.0 (the version attached) and still received an authentication error.

Javelin 2.0.501.0

Patch for this issue is Javelin-2.0.508.0.zip.  Please contact BC Support for this version or if you are installing a GA version AFTER March 5, 2019, please ask BC Support if this version made it into your downloaded GA Version.

Video URL on how to open a Support Case - https://communities.ca.com/videos/5898-demo-how-to-open-a-support-case
You can download the latest version of TDM by following the directions in this document: https://comm.support.ca.com/kb/How-to-Download-Test-Data-Manager/KB000009671.    
To contact support, go to https://www.ca.com/us/services-support/ca-support/contact-support.html.