[Green crosses on minimap]

I am using viewer 3 and sometimes avatars apear on my mini map as little green crosses (instead of the usual up or down arrows). What does this mean?

[SL crashes seconds after login.]

 

When i login to SL, it crashes after around 10 seconds, even if i doin't touch anything.

I have tried manually deleting my cache and restarting my computer a number of times and it has made no difference. SL works completely fine on my other computer (which uses the same internet connection).

The OS is windows Vista

 

Any advice?