Both Firestorm and the SL viewer are closing as it's loading the world. Alts can log in fine.

[Rolig Loon]

It is possible for a buildup of too many notifications to cause Firestorm to disconnect during or shortly after login. If you experience such disconnections repeatedly on Firestorm, then follow the instructions under “Firestorm Logs Out During Login” here.

[Rolig Loon]

It is possible for a buildup of too many notifications to cause Firestorm to disconnect during or shortly after login. If you experience such disconnections repeatedly on Firestorm, then follow the instructions under “Firestorm Logs Out During Login” here.

[valerie Inshan]

Both your avatars may share the same home, but not the same cache files on your computer. Your main maybe has corrupted files while your alt has not. Clearing the cache from outside SL FOR THE PROBLEMATIC AVATAR ONLY can get you fixed. 

http://wiki.phoenixviewer.com/fs_cache_clear

[Jonathan Sivocci]

If it's crashes click, Check I'ms, and close all your notifications and messages you have pending in the upper right corner of the viewer, wait a few seconds and then close the viewer and then Log back in, should work fine then. 

[MartinRJ Fayray]

Hello,

also check your graphics card software (NVidia Control panel, CCC or something like this) if it's set to using the correct graphics adapter for Second Life.