Do not install 2.26 on elastix, the updates on 2.26 are unrelated to the elastix version. The Elastix version has some feautures disabled and replaced with native elastix features (phonebook, recordings, popups).
Your problem must be related to those modifications, I cannot tell you what is wrong exactly as there are missing details on your description. In 2.26, after entering extension and password what happens? Are you prompted again? Or it times out waiting to connect? There is a significant difference between the two behaviors (if you are asked again, then you are entering wrong credentials, if it times out, then the client cannot connect to the fop2_server via tcp/4445)
Anyways, if you use Elastix, stick with 2.25
