I've found something similar and I have soapUI 4.0.0 to compare against.
At work I'm behind a proxy that 4.0.0 can/does authenticate against.
using the same settings in 4.5.1, I keep getting the 407 Proxy athentication error
I've tried
1.the Authenticate preemptively setting on Preferences -> HTTP Settings
2.Setting the AUT fields on the Message Request screen
3.Setting the TestCase Credentials (little key icon)
The message Request in 4.51
GET http://www.eat.businessdata.govt.nz/data/app/ws/rest/companies/entity/search/v1.0/acme HTTP/1.1
Accept-Encoding: gzip,deflate
Authorization: CRD20SLZtSZCbvhc:36/c5vLvy16HHpvGFrrmmsDCvP6Bc3f84dO5ESyJhGw=
Date: Fri, 02 Nov 2012 15:51:19 NZDT
Accept: application/xml
Host: www.eat.businessdata.govt.nz
Proxy-Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.1.1 (java 1.5)
Cookie: BCSI-CS-8dc9b05bc1f5ebb6=2
Cookie2: $Version=1
Cookie: BCSI-CS-8dc9b05bc1f5ebb6=2
Cookie2: $Version=1
Proxy-Authorization: NTLM TlRMTVNTUAABAAAANQIIIBAAEAA6AAAAGgAaACAAAABEAEgALQBBAFUARAAxADAANwAwADMAVgBHAFAAUgBPAFgAWQBCAEMAVwA=
Cookie: BCSI-CS-8dc9b05bc1f5ebb6=2
Cookie2: $Version=1
the message request in 4.0.0
GET http://www.eat.businessdata.govt.nz/data/app/ws/rest/companies/entity/search/v1.0/acme HTTP/1.1
Accept-Encoding: gzip,deflate
Authorization: CRD20SLZtSZCbvhc:hC2KPsRt7AveUX0h6yUBcJbWaQYpsBRzg7s37FnNr2o=
Date: Fri, 02 Nov 2012 15:53:18 NZDT
Accept: application/xml
Proxy-Authorization: Basic Zmxvd2VyaDpIYXJsYTIwMTI=
User-Agent: Jakarta Commons-HttpClient/3.1
Host: www.eat.businessdata.govt.nz
Proxy-Connection: Keep-Alive
Where do all the Cookies come from and how do I set the Proxy-Authorization: Basic in 4.5.1
thanks