Table Based Login Issue

I recently had an issue where only my dev PC could login to a newly created site created with FM Studio. I was utilizing a table based login and everything was working perfectly on my dev PC, but any other PC the login screen would simply refresh index.php. I even had an error message binding on the page that would not reflect any change.

I was initially having the problem myself until I found a post giving instructions to edit line 4 of the FMStudio_Tools.php file. Basically, this is the code that determines the page that will load after a successful login.

What I found out was that on the PC's that could not login I had to manually go to the "redirect" page first (mycalls.php). The page did not load and simply redirected me back to index.php (the login page). Once I did this I could login fine using index.php as normal.

Any ideas as to what could cause this behavior? It's obvious now the reason that I never experienced the issue on my dev PC was because I was previewing the mycalls.php file many times over the course of designing the page!!