[R] Attempting to update from R 2.14 to 2.15

[John Kane]

I am very new to Linux so I probably am doing something stupid but I cannot seem to update to R 2.15

Using Ubuntu 12.02 Precise Penguin

I realise that debian packages are not updated regularly so I tried to follow the insructions at the R-site

So far, I have modified /etc/apt/sources.list to read

## R CRAN added 2012-06-12
deb http://probability.ca/cran/bin/linux/debian squeeze-cran/

Issued command:   sudo apt-get update

RESULT
W: GPG error: http://probability.ca squeeze-cran/ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 06F90DE5381BA480

Ubuntu seems to  have happily run through all the other updates with no problem
Any suggestions?

Thanks 
John Kane
Kingston ON Canada

 sessionInfo()
R version 2.14.1 (2011-12-22)
Platform: i686-pc-linux-gnu (32-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_CA.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_CA.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=C                 LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_CA.UTF-8 LC_IDENTIFICATION=C       

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

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