I appear to be having a problem with RTX and which memory model it is compiled under. I am using the c166 on an ST10F269. This part has a number of flash blocks. I am trying to put a bootloader in blocks 0 and 1 with the remainder of my code in blocks 2,3,... Therefore, I have setup the code as described in some knowledgebase articles to have a jump table from the real interrupt vectors in the boot sector to the relocated jump tables in block 2 (or 3) using the VECTAB linker command. I am using the LARGE memory model to compile all my code. This all works fine for some versions of my code, but others seem to have a problem starting up RTX. I started with my vector table at 0x20000 and had the problem (with only some code versions). Then, I moved it to 0x19000 and the problem went away on the code versions I had problems with. Now I don't know why it works one way and not the other. The problem code seems to die at location os_start_system(). Should I be using the HLARGE model? It is not clear to me whether you have to use the HLARGE model if your constants are further away from your RAM than 64K. Thanks for the help.