Error - function cannot be executed

What causes this issue?

You wanted to reassign a sub-tree so that it would cause other top
positions to be created within the same program structure. Only one
top position is allowed in structure maintenance of investment
programs.

System Response

The function is not carried out.

How to fix this error?

Create additional top positions using the correct function in the
Capital Investment Programs Menu.

Error message extract from SAP system. Copyright SAP SE.