The error message occurs if the length operand value is not yet defined. Even if the statement that defines it occurs before the reference, if the statement has not yet been resolved, the defined value is not yet available.
Processing of statements such as EQU and DC can be deferred and retried after the first pass is complete, allowing forward references, including the first operand to EQU and length or duplication expressions on DC. However, the length operand for EQU must be already defined. The message explanation could probably be improved to clarify this point, so we will look into updating it. In this case, the value of either LPMED_LEN or the duplication factor on the DC has not yet been resolved, so if the DC is included the length cannot be evaluated until later. Apart from unresolved duplication factors or lengths within the area whose length is being taken, another common reason for lengths not being resolved is that the alignment of an item within the area is stronger than the alignment of the start of the area, and the alignment of the start is unknown because of a previous unresolved definition. This problem can be avoided by specifying DS 0D or similar before the start for alignment. Jonathan Scott, HLASM IBM Hursley, UK
