I need to display a bitmap over a label or to put it this way: a label should never overlap a bitmap.

But even if the bitmap is defined in the screen section behind the label or is displayed seperately after the label the label overlaps the bitmap.

Is there a solution for my problem ?

Issue - the label overlaps the bitmap .. I do not believe you can change that behavior. You may have some options using RGB colors and the TRANSPARENT property for labels. One other thought was - when you want to display a BITMAP over a label, consider using a push-button - push-button have a bitmap property and can have text and a tool tip. You would modify the label to not be visible and display your push-button.

My example below using the OK bitmap Acu provides in the AcuBench example project. For the label I use RGB colors and transparent. When displayed, the first label has it where you will see the last letter in the table title displayed on top of the bitmap.

03 Screen1-La-2, Label,
COL 16.60, LINE 3.30, LINES 3.20 CELLS, SIZE 6.10 CELLS, COLOR IS 257,BACKGROUND-RGB H#00C0C0C0, FOREGROUND-RGB H#00400040, ID IS 5, CENTER, LABEL-OFFSET 0,
TITLE "Label", TRANSPARENT.
03 Screen1-Bt-1, Bitmap, TRANSPARENT-COLOR 16777215,
COL 20.80, LINE 3.10, LINES 32, SIZE 61,
BITMAP-HANDLE bmpbtn-bmp, BITMAP-NUMBER 1,
ID IS 6.
Without RGB and transparent the code below you see the label background color on top of the bitmap.
03 Screen1-Bt-1a, Bitmap, TRANSPARENT-COLOR 16777215,
COL 35.50, LINE 3.10, LINES 32, SIZE 61,
BITMAP-HANDLE bmpbtn-bmp, BITMAP-NUMBER 1,
ID IS 9.
03 Screen1-La-1, Label,
COL 31.00, LINE 3.40, LINES 2.10 CELLS, SIZE 5.30 CELLS,
ID IS 8, LABEL-OFFSET 0,
TITLE "Label".

I hope this helps.