Is your sim in that box a Japhar sim ? If it's a Japhar Sim, it would do this if the sim is not programmed for the DM800HDse v1, or if the sim was not properly programmed. If it's not a Japhar, then it will naturally give this error of wrong sim.

So if it's a Japhar you can always flash the box with the image below again,

Image : http://www.ourdreambox.com/ubbthreads.php?ubb=showflat&Number=18363#Post18363

then without rebooting flash the ALLSIM SSL

SSL : http://www.ourdreambox.com/ubbthreads.php?ubb=showflat&Number=290#Post290

Turn off the box and then insert the old sim in the box, take the Japhar and insert it (with the sim plastic it came with) in the correct frontpanel slot and have it flashed with the JAM second option (in Plugin), at the end of the list you will have the FrontPanel Flash DM800HDse v1 v6 (up or down slot, put it right with chip first looking down).

You need to read what the software shows on the screen during flashing of sim to be sure to know what is happening (take a photo and post here so we can read the messages during programming of the sim).

TS