[BioC] 'Error in shell.exec(url) : file name conversion problem' in rtracklayer package

[LiGang]

Dear list, 

I'm using the 'rtracklayer' package and ran into some problems.

         
#===========
	library(rtracklayer)
        browserSession()->toto
	browserView(toto)  
#===========
Above codes work well and show the right webpage.

			
			
however the following code (the last statement) does not work and give the 
error of 'Error in shell.exec(url) : file name conversion problem'
			
#===========
            browserSession()->toto
            ucscTrackModes(toto)->togai
            tracks(toto)->toto2
	    tracks(togai)<-sample(toto2,3)
	    browserView(toto,track=togai)
#===========
			
			
Any suggestions? Thanks!
			
			
sessionInfo()
			
R version 2.8.0 (2008-10-20) 
i386-pc-mingw32 

locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United 
States.1252;LC_MONETARY=English_United 
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

attached base packages:
[1] grid      tools     stats     graphics  grDevices utils     datasets  
methods   base     

other attached packages:
[1] Rgraphviz_1.18.1  graph_1.20.0      rtracklayer_1.2.1 RCurl_0.91-0      
Biobase_2.2.1    

loaded via a namespace (and not attached):
[1] Biostrings_2.10.2  cluster_1.11.11    IRanges_1.0.3      lattice_0.17-15    
Matrix_0.999375-16 rJava_0.6-0       
[7] XML_1.98-1 
			
			
LiGang