Another process is running for update &1 -> &2

What causes this issue?

While a conversion is running, you cannot start any further processes
for the test run. Depending on the size of the dataset in the system,
this process can last a long time.

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?

Check whether all the conversion processes in the corresponding system
are complete (online or background processing), or whether they have
terminated due to a program error. If a process has terminated
abnormally, first solve the error and delete the conversion log, then
restart the process.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.