I am using Autonumber to assign project numbers with a format 07-####, every
once and a while it will skip a number example 07-1030 then it skips to
07-1032. How can i go back to assign the missing number?
You can't.
Autonumbers are NOT suitable for this purpose. An Autonumber has one
purpose, and one purpose only: to provide an almost-guaranteed (there
are bugs) unique key. They are NOT guaranteed to be gapless and can
even become random (say if you Replicate your database).
If you're getting the 07 from looking at today's date, that will also
change to 08 next January - renumbering all your projects!
Instead, I'd recommend using VBA code to store this data in a Text
field. I have code from the Access Developer's Handbook to do this,
but it's copyrighted and I'm reluctant to post it for that reason.
Basically, you need a table with one record, for the next available
sequential number; the code would open this table exclusively,
determine the value, increment it, store it back into the table, and
return the retrieved value back to your Form to update the project
number.
John W. Vinson [MVP]