Reformat the value to be:
Are you using Galaxy or running the tool command line or both? I see your other post at Biostars where the command-line was used: https://www.biostars.org/p/259182/
If you are having problems with the Galaxy version, please make sure that the most current version of Galaxy (15_07) is being used along with the most current version of the Blast+ tool wrapper (0.2.00).
Publication for the Blast+ wrapper in Galaxy: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4557756/
Thanks, Jen, Galaxy team