Pointer to a structure can not be assigned to uint8_t*

Hi guys.

I have the following problem. In my code I have to assign a structure pointer to uint8_t pointer so I can write into the structure byte by byte. Both are pointers of that point to data of different types. Why I cant assign them each other. I am using IAR embedded workbench free size limited version. I tried with other compilers and there was no such problem. 

Here is the scenario:

I don't understand where am I wrong. Please help!