When upgrading a database application to a newer version of 4D, a compile of the application code may not reveal all code execution problems. 4D commands can be included in externally stored documents, such as 4D Write or Quick Report templates and out of date commands will not reveal themselves until execution time.

For example, as the need arises, 4D will make changes to syntax or change the parameters between versions. These changes will be caught in the application code during a syntax check for correction. However, code stored in external files, such as in 4D Write or Quick Report templates will not be checked and the changes will not show up until the code is executed. The catch will show up as an error message such as "...error on line 19 during the EXECUTE command..." That is because 4D commands embedded in templates are executed internally at runtime using an EXECUTE command.

To avoid such an error, whenever upgrading to a newer version of 4D checking the commands used in templates for possible update should be placed on an upgrade checklist.