Рекомендуют сделать следующее:
Maxim Ganetsky (developer):
First, calm down. IDE needs FPC sources in order to create an event and cannot find them.
Second, I reproduced the bug.
It is reproduced with default environmentoptions.xml file (attached).
If I change the following line in this file:
<FPCSourceDirectory Value="h:\lazarus\fpc\2.4.3\source">
so that FPC source path begins with uppercase symbol, i.e.:
<FPCSourceDirectory Value="H:\lazarus\fpc\2.4.3\source">
it starts to work OK.
Until this bug is fixed you *MUST* set correct path to FPC sources in Environment->Options (with the help of according open file dialog or by hand by changing disk name to uppercase) and then run Environment->Rescan FPC source directory. This will fix your issue.