Hi Becky
I assume you are using Windows and the secr Windows binary had not been updated to 2.10.0 on the particular mirror site you used at the time you tried. I tend to use 'Install packages' from the Packages menu of the R GUI, and it worked for me from the Auckland mirror just now on this machine. I suggest you try again, try a different mirror, and if all else fails get the zip file from https://cran.r-project.org/web/packages/secr/index.html.
Murray
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