103 101 99 97 93
This implementation is based on primo's comprehensive description of the algorithm he used.
for(e=l=x=prompt(g=1e5);--g;l=(x>1?y=1-1/x:-(y=x-1))*l+y/g) e=1+e/g*x; alert([e,x>0?l:"ERROR"])
- Trying to catch Perl. Stole a byte back from primo by copying his branch. :)
- 2 more bytes courtesy of primo.
- Finally, caught primo's version! With primo's help, of course... :)