Total percent = &1%, &3, period &2, source assignment &4

What causes this issue?

You have entered distribution rules that only settle &V1&% or amount
rules. This applies to view/version/settlement type &V3& in period &V2&
and source assignment &V4&.
If you want to carry out a partial activation (sum of the distribution
rules <(><<)>100%) during the summary settlement of investment measures,
you must enter the period in which you want to perform the partial
activation. This is also valid for distribution rules with amount input.
Example:
Lno. Type Receiver Perc. Eq.no. ST SA from to
4 AST Asset 1-0 10.00 FUL 1 10.yyyy 10.yyyy

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

This rule is used just once during partial activation in period 10/yyyy.
If you are using a source structure and source assignment ' ', note the
following:
Source assignment " " is assigned to all possible origin assignments in
the structure you are using. This is even if you did not specifically
use the corresponding source assignment.
Example:
Source assignments (SA) A and B are defined in your structure. You
specified two rules:
SA ' ' 70%
SA 'A' 30%
If you defined a check for exactly 100% in the settlement profile, you
see an error message for source assignment 'B', as this is showing only
70% (from SA ' ').

How to fix this error?

Correct the distribution rules.

Error message extract from SAP system. Copyright SAP SE.