If you are not combining license files from different vendors, the simplest thing to do is make sure you use the tools (especially lmgrd) that are shipped by each vendor.
As lmgrd always correctly supports older versions of vendor daemons and applications, it's always safe to use the latest version of lmgrd and the lmutil utilities.
If you have combined license files from two vendors, you must use the latest version of lmgrd.
If you have received two versions of a product from the same vendor, you must use the latest vendor daemon they sent you. An older vendor daemon with a newer client will cause communication errors.
Please ignore letters appended to FLEXlm versions, i.e., v2.4d. The appended letter indicates a patch and does NOT indicate any compatibility differences. In particular, some elements of FLEXlm did not require certain patches, so a 2.4 lmgrd will work successfully with a 2.4b vendor daemon.