Eventually I suceeded in installing fpc3.
The thing seems to be that it now supports long file names (LFN).
The installation procedure checks for support of LFN by the OS it is installed on.
As my MSDOS 6.0 does not support LFN, it is switched off. However, this also means that by default some required parts are not installed, like the CRT unit. As a result I could not compile my program.
Only after setting the list of parts to be installed such that required parts are installed as well, the compilation with fpc3 on MSDOS 6.0 does work.
The next point is that, due to LFN support and/or UniCode support, the internal structure of TextRec has been changed. This causes a compilation error, since I do access its field "Name" with the StrIComp() function, which expects an array of char, but meets an array of widechar.
When all this has been solved (and anything else that may pop up) I may check for the compiler behaviour with respect to the original problem :-)
Until then, thank you for your support.
MartenR