The first thing to check is that you have the correct version of the add-on for your version of Tecplot. Assuming that you have downloaded the tar file containing the addon libraries (http://tecplottalk.com/addons/ExtPrec/r2/extprec.tar
), then there are many versions of the addon. To figure out which version you should copy, look at the install.log file in your tecplot home directory. This should contain a line
Installing : linuxg248x64.26
which will tell you the version of Tecplot which you installed (there are several lines like this, but only one will have the weird form specifying the specific linux version you installed). Choose the corresponding version of the addon and copy it to lib directory of your tecplot installation. Add the proper entry to your tecplot.add file and you should be good to go.
I hope this helps you,