Fastcat: Target name cannot have a .hist, .ktab, or .prof suffi #25

I followed the example 2 for hpc operations as I got an not enough disk space error when running fastk in single instance.
I completed the commandsfastk and fastmerge and end up with 25 slices. For each slice I have two files, e.g. slice10.hist and slice10.ktab. Now I am trying to apply the command fastcat.
However, it throws the following error:

Fastcat -vht full slice1 slice2
Fastcat: Target name cannot have a .hist, .ktab, or .prof suffi

I tried renaming files to remove the suffix, but it doesnt make a difference and the error persists.

I also tried:

Fastcat -vt full slice1.ktab slice2.ktab
Fastcat: Target name cannot have a .hist, .ktab, or .prof suffi

What am I doing wrong?