this is actually a 5 tank platoon and is based on a modded installation of lockie's latest mission files but here goes.
http://www.mediafire.com/?8f7148uwoyck3zythe actual changes should be easy to transfer to any new files when the next patch is released
Here's the problem with your setup, in the 'common_units.engcfg' file, you're duplicating the 'wer_platoon_htank51' entry (done before by Donken, I think).
// Panther G
wer_platoon_htank51,0,1,wer_htank51,1,wer_htank51,1,,,,,,;
wer_platoon_htank52,0,1,wer_htank51,2,wer_htank51,1,,,,,,;
wer_platoon_htank53,0,1,wer_htank51,1,wer_platoon_gren1,1,,,,;
wer_platoon_htank54,0,1,wer_htank51,3,wer_platoon_gren1,1,,,,;
wer_platoon_htank55,0,1,wer_htank51,3,wer_platoon_inf,1,,,,;
//Panther_G_groups
wer_pantherg,800,0.25,weru_pantherg,1,wer_crew_panther,1,,,,,,;
wer_crew_panther,300,0,weru_tleuten,1,weru_tankman,1,weru_tankman_p,3,,,,;
wer_platoon_htank50,0,1,wer_pantherg,2,,,,,,,,;
wer_platoon_htank51,0,1,wer_pantherg,5,,,,,,,,;
I'd suggest commenting out the entry that you don't want (probably the first one).