How To Fix WL390 - Expression '&' does not contain a date or time or has errors

SAP Error Message - Details

• Message type: E = Error

• Message class: WL - Workflow: run-time messages

• Message number: 390

• Message text: Expression '&' does not contain a date or time or has errors

What causes this issue?

The expression '&V1&' was specified as a reference point for the
deadline calculation for activity no. &V3&. This expression either
contains no (valid) date or no time or contains an error and therefore
cannot be evaluated.
Note: The internal ABAP type of the expression was &V2&, its content
&V4&.

System Response

For the deadlines "latest end, desired start, latest start, desired
end" a warning is logged and a work item is created without these
deadlines.

How to fix this error?

Check the expression concerned in the workflow definition and ensure
that its value is a correct date or a time.
If a work item has been created without (a) deadline(s), you can set
this/these subsequently.

Error message extract from SAP system. Copyright SAP SE.