If there are multiple checks which check_KAV.bat has to handle at the same time, the batch file will fail, because the temporary files are already opened by another process. The following error is in such cases shown as Nagios output:
The process cannot access the file because it is being used by another process.
I've made a small bugfix so multiple checks can be done at the same time:
The modified batch file can be downloaded here -> check_KAV_sqlinst.bat.