What causes this issue?

The asset number &V1& has been determined from the internal asset
number assignment. However, this asset number already exists.

System Response

The System has determined an inconsistency between asset number
assignment and the asset master file. The number to be assigned &V1&
exists already. It cannot be assigned. Processing is terminated.

How to fix this error?

Contact your Systems Specialist.
Check the number range assignment for number range &V3&.
If necessary, assign another number range to asset class &V2&.

Error message extract from SAP system. Copyright SAP SE.