Error acces Lock TABLE in nav 2013

I have 2 reports who uses the same table. (pT_Filter --- TemporalFilter)

The table is in the 50000 range.

There are only a few lines referred to this table.

REPORT 50001

[b]OnPreReport[/b]

pT_Filter.RESET;
IF NOT pT_Filter.GET THEN
  pT_Filter.INSERT;

pT_Filter."Date From CG21" := v_periodFrom;
pT_Filter."Date To CG21" := v_periodTo;
pT_Filter.MODIFY;


[b]OnPostReport[/b]

pT_Filter."Date From CG21" := '';
pT_Filter."Date To CG21" := '';
pT_Filter.MODIFY;

REPORT 50002

[b]OnPreReport[/b]


IF NOT pT_Filter.FINDFIRST THEN
  pT_Filter.INSERT
ELSE BEGIN
  pT_Filter.RESET;
  pT_Filter.LOCKTABLE;
  pT_Filter."Date from CG19" := text_from;
  pT_Filter."Date to CG19" := text_to;
  pT_Filter.MODIFY;
  COMMIT;
END;

Sometimes, when I try to execute from differents users. (Or either from same user both reports at the same time). Nav throw me an error from this table is Locked

Maybe there is a problem in report 50001, but I cant explain myself why is this happening.