R help - Jun 2007 - read.xls problem

Hi to all,
I have a strange problem
There was a Excel file with 5 sheets
I deleted sheet 2 and 4.
as all the times before I tried to read the sheets with
data1<- read.xls(excelfile_2,sheet=1, as.is = TRUE ,verbose=FALSE, 
perl="C:/perl/bin/perl.exe")
data2<- read.xls(excelfile_2,sheet=2, as.is = TRUE ,verbose=FALSE, 
perl="C:/perl/bin/perl.exe")
data3<- read.xls(excelfile_2,sheet=3, as.is = TRUE ,verbose=FALSE, 
perl="C:/perl/bin/perl.exe")

but only the folloing code reads the sheets well
data1<- read.xls(excelfile_2,sheet=1, as.is = TRUE ,verbose=FALSE, 
perl="C:/perl/bin/perl.exe")
data3<- read.xls(excelfile_2,sheet=3, as.is = TRUE ,verbose=FALSE, 
perl="C:/perl/bin/perl.exe")
data5<- read.xls(excelfile_2,sheet=5, as.is = TRUE ,verbose=FALSE, 
perl="C:/perl/bin/perl.exe")

Does anybody know whether this is normal?
 I never had this problem before. And if it is normal I wonder about how 
to find the sheet numbers

Regards Knut