When you have created Validations and/or Substitutions in SAP, behind the scenes when you save them; the system transforms them into real ABAP code so then when executed them ends up executing ABAP code.
When you transport them into any other environment, you will see that at the end of the transport import the system is regenerating code. But in most of the cases you will still need to regenerate that code for those Validations and Substitutions manually otherwise you could face certain issues (OSS Note 2512768 explains this). These are some of the issues you could face. Ex.

• When you try to post a Journal Entry with FB50, 60 or similar; it could be annoying that the system will tell you that it needs to run a regeneration program and you need to start over. This could happen twice. If a user receives this type of error he/she will probably freak out and end up raising an incident for something easy, quick to fix and that could have been prevented. Error GB073 – Generation successful, but you must call up the function again.
• Other type of postings attempts from other modules like MM, could directly fail as those interfaces do not try to trigger these regenerations.

So to avoid yourself any issues, any time you transport Validations and Substitutions; right after the transport went in, you should run program RGUGBR00 (with SE38) to regenerate the ABAP Code for them.

To play safe you should activate all “generate” options * on “Appl area” and “Callup”.

This not only applies to FI type of Validations and Substitutions, it also apply to all other types that exists in other SAP Modules like PS, SL, EC-CS, etc. So, this recipe should also be followed for those as well.

Other info on Validations / Subtitutions
842318 – Frequently asked questions about validations and substitutions