By default, Free Pascal (actually, the linker used by Free Pascal) creates libraries that are not relocatable. This means that they must be loaded at a fixed address in memory: this address is called the ImageBase address. If two Free Pascal generated libraries are loaded by a program, there will be a conflict, because the first library already occupies the memory location where the second library should be loaded.
There are 2 switches in Free Pascal which control the generation of shared libraries under Windows:
Generate a relocatable library. This library can be moved to another location in memory if the ImageBase address it wants is already in use.
Specify the ImageBase address for the generated library. The standard ImageBase used by Free Pascal is 0x10000000. This switch allows changing that by specifying another address, for instance -WB11000000.
The first option is preferred, as a program may load many libraries present on the system, and they could already be using the ImageBase address. The second option is faster, as no relocation needs to be done if the ImageBase address is not yet in use.