I think there might be some confusion being generated due to different numbers being calculated by different calls. Just to make it clear I am including the time of running for both.
23:12:42

exec getabnweight 256000 1
23:12:42

{
"Command": "getabnweight",
"version": 1.2,
"weight": 262754.2036458333,
"total_required": 259210,
"coin_age_data_pre_select": "6000.8578(1.01)=[6081.39] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n10000.0010(1.01)=[10135.65] depth=213, \n",
"weight 256000.00": 259472.5925925926,
"total_required 256000.00": 256000
}
And then
23:13:06

exec createabn 256000
23:13:06

{
"Command": "createabn",
"xml": "
ABN2a09a4304a2240e192290278901c6a333eaec51e333f84aeaea31709b2351c46H/aHFUnR35zLCtcIZcBEuU8HhTJeUE/aQ2JyXL4F1oH2fMGaoXpKj2tWbtmKnGo504wBmPUBHMPv/po153CRh/0=BPZZtoNfm2qVNt9muG9KB6A4MZb9msXciS256000",
"err": "CreateABN::Fail::(Create Transaction) Insufficient funds.::TargetWeight=259473, UsingBBP=256000.00, I=25, NeededWeight=256000, GotWeight=239299.60",
"age_data": "6000.8578(6081.39),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),10000.0010(10135.65),3209.3113(3281.61),",
"tx_create_error": "CreateABN::Fail::(Create Transaction) Insufficient funds.::TargetWeight=259473, UsingBBP=256000.00, I=25, NeededWeight=256000, GotWeight=239299.60"
}
Obviously either exec getabnweight is too high (by almost 20K) or createabn call is too low.
If you want, you can compare and match the coins in parentheses across the two outputs, and see if you can find the two coins that are missing - and let me know that you think 2 coins are missing from one of the two commands.