Steps to reproduce:
New Item
Item Name Test-Add-Credentials
Source Code Management, Select svn
Repository URL: https://mysvn.repository.com
Credentials double click [add button]
[Popup] Select Jenkins, double click
[Popup] Jenkins Credentials Provider: Jenkins
Select "Global Credentials (Unrestricted)" From the dropdown list for DOMAIN
Select "Username with password" from the dropdown list KIND
Select "Global (Jenkins, nodes, items, all child items, etc) from the dropdow list SCOPE
write "user" at the USERNAME
write "password" at the PASSWORD
do not write anything at ID
write "Testing adding credentials" at DESCRIPTION
double clkie [ADD ] button

obtains a grey popup window with "ERROR" as a window title, and nothing else. There is no error on the server side