local BLAST error: BLAST Database error: Error: Not a valid version 4 database I want to use a local blastn command to BLAST a multifasta file ~700 sequences using following command: blastn -db nt -query fasta_all.fasta -num_alignments 2 -out fasta_blasted.txt but I receive error :BLAST Database error: Error: Not a valid version 4 database.

I use a local nt database which I downloaded today (11th of May 2020) by running update_blastdb.pl --decompress nt [*]. I downloaded this but I did not do any post-processing and just the "raw" download files are in the folder (see image below which shows only a part of the files)



The blast+ I downloaded and installed is ncbi-blast-2.10.0+-x64-linux.tar.gz from https://ftp.ncbi.nlm.nih.gov/blast/executables/blast+/LATEST/

So, both database and blastn version should be the latest. It probably has something to do with either the version of the database or the software, but as it both are the latest version, I find it strange that these would not be compatible. Any ideas what causes this error?
first I recommend you to check your downloaded data with md5 to be sure there was no problem with that step. How many files did you download?
Also I was curious if you had another BLAST+ version installed on your computer. Be sure that blastn is called is a version corresponding to the database you are using.