I am using a 64-bit machine, with the latest version of R (3.1.2), the latest RStudio version (0.98.1091) and the latest JAVA (Version 8 Update 31).
I tried to require r
The architecture of Java you get for install from the regular Java download web page depends on the architecture of browser you’re using (32-bit or 64-bit) when you download it. This happens without any fanfare. Try the Java manual download page, select the 64-bit version of Java for your OS, install it, and then (after restarting R) try your R packages again.
I think the problem on this occasion is that your Java is 32-bit, whereas your R is 64-bit. This is why you get a R and Java have different architectures
error.
In order to check what your Java version is on Windows type:
java -d64 -version
on the command line as it is mentioned here.
I think that once you install the correct Java version i.e. the 64-bit on this occasion then loading your xlsx
library will work!