Invalid start position: &

What causes this issue?

With the aid of account operations, you can insert or delete characters
into or from all selected account keys at specific points.
o With I/<start_position>/<insert_string>, it is possible to insert
characters into the selected account keys at a certain point. For
example, with 'I/03/W1', the string 'W1' is inserted into all
selected account keys at position three.
o With D/<start_position>/<length_del_string>, it is possible to
eliminate characters from the selected account keys at certain
points. For example, 'D/03/02' will cause two characters to be
deleted from all selected account keys, beginning at position three.
In the process, <start_position> is specified as two characters, e.g.
'03' for position 3. The current length of the G/L account field may
not be exceeded, either explicitly or implicitly, by inclusion of
<insert_string> or <length_del_string>. Thus for example,
<start_position> of 'I/09/ABC' is not allowed for a 10-character G/L
account field, whereas 01 - 08 is permissible.

System Response

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

How to fix this error?

Please enter a valid start position.

Error message extract from SAP system. Copyright SAP SE.