My code compiles fine when using Visual Studio 2013, but when converting it to VS15, I get this error:
Error LNK2001 unresolved external symbol _snprintf FEBio2 C:\FEBio2_15\VS2013\mkl_core.lib(mkl_aa_fw_device_threading_params.obj) 1
Intel people have suggested removing VS2015 and installing from scratch rather than trying to deal with the in-place upgrade scheme. Although I have a better than average USA internet connection, this will take a day or two.
Microsoft have suggested opening up the VS2015 Modify after a partial upgrade and completing addition of the offered Windows Kit \10\ if it shows such an option. In my experience, this doesn't solve the problem of the LIB and INCLUDE environment variables remaining on older Windows Kit \10\ folders which have been cleaned out. You can copy items back into the folders which are shown in the environment variables if you like.