I would like ask you few questions to understand the issue.
1. Did you try to open the hyperlink from SolarWinds server?
2. Did you confirm that the website is working as expected?
3. Did you define any custom string, that should be present in the website?
4. Are there any forwarding/redirection configured for the website?
The last question is very important, because HTTP Form Login can receive an error when there is redirection on htaccess or in hosting service.
You can also try to disable checking for redirection inside the template and try the test again.
I hope this will help and I will wait for your reply.
IT-Indago Ltd. - Authorized Reseller & SolarWinds Certified SCP Professional