The reason for the error is that the STL file contained the string "STLB__ASM__216.00.01.1000" in the solid name field. This field is used by STL2VRML function to define the corresponding VRML object DEF name - and dots (".", 0x2e) are not allowed in VRML97 DEF names.
1. I assume that your STL file is an ASCII STL file. Open the file in any plain text editor (for instance MATLAB Editor) and replace dots in the name at the first line of the file with something else, I suggest underlines (_).
Most probably, your first line looks like this:
Change it to:
(Or, better, to something meaningful for you, like: solid Flywheel_1 )
Valid characters for VRML node names are described in the end of A.3 Appendix of the VRML97 standard:
Of course, you can correct the file also by making sure that your CAD tool doesn't export STL files with dots in solid names.
2. I would like to ask you a favour - please let me know which software, and under which circumstances exported your STL files with dots in solid names. We need this information so that we can make STL2VRML more robust. For instance, I am interested if the "STLB__ASM__216.00.01.1000" name directly corresponds to some CAD part name, etc.
Good luck and thank you for your diagnostic info.