There are also some messages in the bottom report window:
Reading keyword line: *NODE
Reading keyword line: *ELEMENT,TYPE=C3D20R
An item with the same key has already been added.
I successfully imported this mesh to FreeCAD so the file itself is correct. It may just contain some unsupported node/element definition syntax but I’m not sure what causes the problem.
*edited
it seems not related to node number or merging, the input file contains tabs before node and element numbers. maybe CGX is accepted these but PrePoMax is not.
Right, that’s what I suspected - the specific format of this input file can’t be read by PrePoMax. Importing the file to FreeCAD and then exporting it back fixes the format and the file can be imported to PrePoMax. However, I’m not sure which tabs or spaces are causing the problem.