Are you seeing an error message?

You have two If's, but only one End If, and you've got an Exit Do outside
the loop.  It's a good idea to get used to indenting your code inside any
If, Do, While, or With block.  Doing that makes it easier to read, and
easier to spot errors like this.

Rob

Lots of reasons..

First off, EVERY module should begin with these two lines

  Option Compare Database
  Option Explicit

In the IDE, click on TOOLS/ OPTIONS .  On the Editor tab, everything should
be checked except the first check box "Auto Syntax Check".

--------

** You didin't declare these variables:

   rstPOServices
   lngSOCount
   intTrans

BTW, the variable "intTrans" should be declared as Boolean (bolTrans), not
Integer because you are setting it True/False.

** The nesting of the IF()'s and the DO loop is wrong. And the "EXIT DO" is
outside of the loop.

** "lngThisVend" needs to have a value set before you start the loop. On the
first pass , it is NULL. The line before the DO statement should probably set
the value to the field value in the first record of the recordset. The next
line would be
  rstSToOrder.MoveNext

** The first "CommitTrans" is in the wrong place and whould be deleted. The
2nd "CommitTrans" should be moved to just after the line
   rstPOServices.Update.

**You do not have any way to do a ROLLBACK, or a way to check if a ROLLBACK
is necessary.

** In lines like this

  rstPO!Order_Date = [DateIn]

if [DateIn] is a field in the recordset "rstSToOrder", then it has to be
fully qualified:

  rstPO!Order_Date = rstSToOrder![DateIn]

You need to decide if you want to commit the changes after each insert
(.AddNew/.Update), or after ALL inserts have been made. That will determine
if the "BeginTrans/CommitTrans" statements are inside or outside of the DO
loop. I would suggest committing after each insert. And you need a way to
know which records were not inserted (more code).

Some error trapping code would be nice....

HTH