Hi 100bure,
How about converting you Autoexec Macro to a vb Function using the build in conversion (Tools, Options, Convert...). Then Make another Autoexec Macro which has just a runcode command to run the Function you just created. This was you can get more control over things. Then put an IF staement into the code you are trying to run only once. Make the IF statement perform a test on the contects of a table (eg DlookUp(...the entry in the table = a specific thing). If the contents do = this specific thing, make the code run an update query on the table so the contents become something different. This way, on first run, the table entry changes and the code will therefore never run again.
Its a bit of a lumpy solution bit I know it works. I've used it before with a Autoexec macro to keep on showing a form (which the user has to press OK or Cancel to Accept licence conditions). Pressing Cancel shuts down the database, pressing OK causes the table to be updated and the code never run again.
Hope this helps, jobo123