Problem simplified by removing discrete constraints

What causes this issue?

An error occured while the optimizer was trying to find a solution. This
error is described in a separate message.

System Response

Due to the profile settings for unsuccessful solution determination, the
discrete constraints are removed and the optimizer makes another attempt
to calculate a solution.

How to fix this error?

If you would like the optimizer to respond differently to errors, you
should change the settings in the optimizer profile.

Error message extract from SAP system. Copyright SAP SE.