Marco Malziotti , which browser are you using? Esp. the latest Chrome/Edge browsers give issues with Vugen. OT has patches available.
An alternative might be to use FireFox or use the chromium version installed with VuGen. To use this chromium version, do not select a browser, but an application. You can find chromium in the VuGen installation folder under .../bin/chrome/chrome.exe

You can also download a relocatable chromium version from the internet and use that one, but you have to experiment which version will work.

 JHF Remmelzwaal Now I have Microsoft Windows 11 Pro and I got that error using Chrome version 130.0.6723.92 (64-bit).

Using Chromium version 108.0.5359.125 (64 bit) I get the following recording logs
[Proxy Recording (4d58:3de0)] Trying to connect to smauth12.retecert.postecert:443/.../creds.ntc
[Proxy Recording.Error (4d58:5084)] Exception is caught during async receive, message=Remote server error: (401) Unauthorized
...

Using Firefox version 132.0 (64 bit) I get the following recording logs
[Proxy Recording (5470:15a4)] Trying to connect to smauth12.retecert.postecert:443/.../creds.ntc
[Proxy Recording (5470:2978)] Client request from @ 192.168.1.17:18333
[Network Analyzer (5470:4fc4)] (Sid: 8) Server -> Client : 202 bytes (SSL) (Service=HTTP)
[Proxy Recording.Error (5470:121c)] Exception is caught during async receive, message=Remote server error: (401) Unauthorized.
...
[Proxy Recording (5470:2a70)] Trying to connect to incoming.telemetry.mozilla.org:443/.../...
[Proxy Recording.Error (5470:2a70)] Cannot add request header message:L'intestazione 'date' deve essere modificata utilizzando la proprietà o il metodo appropriato.
Nome parametro: name

Using Edge 130.0.2849.68 (64 bit) I get the following recording logs
[Proxy Recording (2668:4ac8)] Trying to connect to smauth12.retecert.postecert:443/.../creds.ntc
[Proxy Recording.Error (2668:52c8)] Exception is caught during async receive, message=Remote server error: (401) Unauthorized.

I remember that when navigating manually with any browser, once you type the address X (which I indicate in the "URL address" field in the "Recording Mode" section of the "Start recording" window), you are redirected to the URL Y which shows a login pop-up. The URL Y is the one that in the recording logs I find with "Remote server error: (401) Unauthorized" ( https://smauth12...). Login pop-up does not appear in recording mode.

Thanks.

Marco Malziotti

Marco Malziotti , It might be that the login procedure is using some 'secret' header value that will change each time to try to start a login sequence. To pickup those values you have to capture them in the first request and send them in the next request. This is called correlation and is fundamental to scripting at this protocol level.

You might also find sometimes header values generated by JavaScript like GWT or OAuth headers. Than you need to use some JavaScript to generate the right value.

One way to address this is to open your browser and open Dev. Mode (press F12), enable Network trace and do your login. Look and compare the trace you just made with your LR recording and find all places with different header values and differences in URL. Most of them needs to be parameterized. (Except cookies, those are handled automatically, BUT sometimes a cookie value is used in another header as well). 

JHF Remmelzwaal Maybe I didn't explain myself well, the registration process does not record any calls! The redirect is on the first call.
I attach two videos:
energentspa-my.sharepoint.com/.../Egxx_E9kN6VFhcS98GGT_hkBPuPhIU2slHSMa3X91swamA
- recording from VUGen: PianetaUP-recording-LoadRunner.mp4
- manual access to the page: PianetaUP-diretto.mp4
Thaks.