[R] Sweave special characters problem

[Bunny, lautloscrew.com]

Dear all, 

I use Sweave to create my reports. Unfortunately my script crashes whenever I my R code contains special characters like umlauts. 
Is there a way to to escape special characters in Sweave... This is the line that crashes Sweave:

gl_bybranch = ddply(new_wans,.(period,Branchen), function(X) data.frame(Geschäftslage=mean(X$sentiment)))

Unfortunately I can't just rename it, because I it´s displayed in the legend of graphics later on.

Thx for any suggestions! 

best 

matt