We are facing a recurring diagnostic issue on a Siemens SIMATIC S7-400 system and would appreciate your support.

System details:
- PLC: SIMATIC S7-400
- CPU: CPU 412-5 H PN/DP
- Configuration: H-system
- Communication: PROFINET IO
- Engineering software: STEP 7 Classic
- CPU status: RUN (no force job)

Problem description:
The CPU diagnostic buffer repeatedly reports the following event:
- Event ID: 16#A090
- Message: “Area length error when reading”

The event occurs cyclically and fills the diagnostic buffer. The CPU remains in RUN, but the error persists continuously.

Observations:
- The issue appears related to PROFINET IO communication.
- No CPU hardware faults are indicated.
- The error repeats at short intervals, suggesting a cyclic read access issue.
- This may be related to an I/O length mismatch, invalid memory access, or PROFINET device configuration inconsistency.

Request:
We kindly request your guidance on:
1. The exact interpretation of Event ID 16#A090 for S7-400 PN CPUs
2. Recommended diagnostic steps to identify the specific PROFINET device or block causing the error
3. Any known issues or Siemens recommendations related to PROFINET I/O area length errors on H-systems