Lmgrd & lmadmin will perform file extension checks on license files which are imported.
They check for .dat, .lic and .txt extension in the whitelist.
If an extension is not found in the whitelist but is found in a blacklist (containing .bat amongst other disallowed extensions) then the file will fail to import with an "Invalid License File" message or "Cannot find license file".
Please note that this applies to Flex net publisher version 11.14 and higher.
To avoid this situation, use any of the whitelisted extensions for license files.