a) GATK version I used:  gatk-4.1.8.1
b) Exact command used: java -jar ~/tools/gatk-4.1.8.1/gatk-package-4.1.8.1-local.jar CreateSomaticPanelOfNormals -V normals_for_pon_vcf.args -O test.vcf.gz
c) Entire error log:

16:00:11.502 INFO CreateSomaticPanelOfNormals - ------------------------------------------------------------
16:00:11.502 INFO CreateSomaticPanelOfNormals - The Genome Analysis Toolkit (GATK) v4.1.8.1
16:00:11.503 INFO CreateSomaticPanelOfNormals - For support and documentation go to https://software.broadinstitute.org/gatk/
16:00:11.503 INFO CreateSomaticPanelOfNormals - Executing as user@x3650m4-2 on Linux v4.4.0-197-generic amd64
16:00:11.503 INFO CreateSomaticPanelOfNormals - Java runtime: OpenJDK 64-Bit Server VM v1.8.0_275-8u275-b01-0ubuntu1~16.04-b01
16:00:11.503 INFO CreateSomaticPanelOfNormals - Start Date/Time: December 21, 2020 4:00:11 PM CST
16:00:11.503 INFO CreateSomaticPanelOfNormals - ------------------------------------------------------------
16:00:11.503 INFO CreateSomaticPanelOfNormals - ------------------------------------------------------------
16:00:11.504 INFO CreateSomaticPanelOfNormals - HTSJDK Version: 2.23.0
16:00:11.504 INFO CreateSomaticPanelOfNormals - Picard Version: 2.22.8
16:00:11.504 INFO CreateSomaticPanelOfNormals - HTSJDK Defaults.COMPRESSION_LEVEL : 2
16:00:11.504 INFO CreateSomaticPanelOfNormals - HTSJDK Defaults.USE_ASYNC_IO_READ_FOR_SAMTOOLS : false
16:00:11.504 INFO CreateSomaticPanelOfNormals - HTSJDK Defaults.USE_ASYNC_IO_WRITE_FOR_SAMTOOLS : true
16:00:11.504 INFO CreateSomaticPanelOfNormals - HTSJDK Defaults.USE_ASYNC_IO_WRITE_FOR_TRIBBLE : false
16:00:11.504 INFO CreateSomaticPanelOfNormals - Deflater: IntelDeflater
16:00:11.504 INFO CreateSomaticPanelOfNormals - Inflater: IntelInflater
16:00:11.504 INFO CreateSomaticPanelOfNormals - GCS max retries/reopens: 20
16:00:11.505 INFO CreateSomaticPanelOfNormals - Requester pays: disabled
16:00:11.505 WARN CreateSomaticPanelOfNormals -

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Warning: CreateSomaticPanelOfNormals is a BETA tool and is not yet ready for use in production

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

16:00:11.505 INFO CreateSomaticPanelOfNormals - Initializing engine
16:00:11.814 INFO CreateSomaticPanelOfNormals - Shutting down engine
[December 21, 2020 4:00:11 PM CST] org.broadinstitute.hellbender.tools.walkers.mutect.CreateSomaticPanelOfNormals done. Elapsed time: 0.01 minutes.
Runtime.totalMemory()=1987575808
***********************************************************************

A USER ERROR has occurred: Cannot read file:///home/user/STR/test_bam/Lin/202012/Mutect2_output/normals_for_pon_vcf.args because no suitable codecs found

***********************************************************************
Set the system property GATK_STACKTRACE_ON_USER_EXCEPTION (--java-options '-DGATK_STACKTRACE_ON_USER_EXCEPTION=true') to print the stack trace.