Codesys v3.5.22.10 - Internal error:System.AggregateException...Value cannot be null...Parameter name: expLValue

hhermsen — Sat, 11 Jul 2026 12:37:34 -0000

I pinpointed down 4 possible causes for this compiler error:

Bare/empty statements (;) standing alone inside an IF/CASE branch — just removed two instances. The optimizer that tries to inline/replace expression statements may choke when a statement has no actual assignment to extract.
A VAR_IN_OUT parameter used directly as a FOR loop's own control variable (FOR X := X TO Y DO)
General deep-nesting complexity — every one of my decode routines has the same shape (IF busy THEN ... FOR loop containing nested CASE/IF chains ... END_IF), and the crash trace consistently shows for loop → sequence → ifst → sequence → ifst → sequence regardless of the code change. This raises the possibility that it's not one specific statement but a structural depth/complexity limit in SP22.x's compiler optimizer — which would mean no small code change fixes the issue. Only restructuring to reduce nesting depth, or downgrading the compiler will.
Something entirely outside my library files — which cannot not ruled out since the exact stack trace was triggered by a Visualization object, in a totally different codebase. This means the same crash signature can come from unrelated causes.

IMHO cause 3 is the most probable one..

Codesys v3.5.22.10 - Internal error:System.AggregateException...Value cannot be null...Parameter name: expLValue

hhermsen — Sat, 11 Jul 2026 12:20:19 -0000

Internal compiler error in SP22.x (expLValue null) — SP21 unaffected — need help isolating root cause
I'm hitting the same internal compiler crash reported here. Same exact stack trace (AssignmentStatementReplacer → CreateAssignmentExpression → ArgumentNullException: Value cannot be null. Parameter name: expLValue), but in my case triggered by a self-written library, not a Visualization object — so this looks like a general SP22.x codegen regression rather than something tied to one specific language feature.

What I've confirmed:

Reverting to SP21 — no issue, builds clean
SP22.x — internal compiler crash during Build > Application, code generation phase, with zero useful location info (no POU, no line number)
check_for_errors/precompile-only passes cleanly; the crash only happens on a real full build, meaning static analysis never sees it coming

What I've tried to isolate the cause (without success):

Removed a suspected pattern involving a VAR_IN_OUT parameter used directly as a FOR-loop control variable, combined with early RETURN inside the loop — crash persisted identically afterward
Confirmed no Visualization Manager or similar object in the project (ruling out the trigger in the linked report)
Used an AI coding assistant (Claude Code) to search for other suspicious patterns — no luck pinpointing the exact statement

Question @codesys-com
Since the compiler gives no location info at all, is there any way to get more diagnostic output from the SP22.x codegen phase (verbose/debug build flags, log level settings, etc.)? Without that, isolating this in a large library means blind bisection — cutting the codebase in half repeatedly until the crash disappears, which is slow and error-prone without official tooling support.

Happy to share the affected project or a minimal repro if that helps CODESYS engineering track it down.

Beckhoff CX9240 : Using Internal EtherCAT Bus

yannickasselin — Fri, 10 Jul 2026 16:24:28 -0000

Now I understand. I always thought this was not supported. I might test it later. Thanks.

Beckhoff CX9240 : Using Internal EtherCAT Bus

eschwellinger — Fri, 10 Jul 2026 14:50:32 -0000

you need just out of this windows rte cx package the internal EthercatMaster device description

Dynamic Images

erik.gerrits — Fri, 10 Jul 2026 13:29:09 -0000

I ran into this issue as well. Here is the fix:

Good example:

CASE iBitmap OF
0 : sName := 'ImagePool.image0';
1 : sName := 'ImagePool.image1';
END_CASE

Bad example (this will only work on the target device, WebVisu will show a blank rectangle):

CASE iBitmap OF
0 : sName := '/home/cds-apps/PlcLogic/visu/image0.png';
1 : sName := '/home/cds-apps/PlcLogic/visu/image1.png';
END_CASE

Beckhoff CX9240 : Using Internal EtherCAT Bus

arj3090 — Fri, 10 Jul 2026 13:15:08 -0000

I installed Linux ARM SL and it recognizes the RJ45 ethernet ports, but I cannot get it to recognize the internal port for the IO cards.

See if application is running

ttvs — Fri, 10 Jul 2026 10:25:07 -0000

Hello,
Is it possible to check if PLC application is running or stopped from linux shell? I am using codesys control for linux arm64sl. Tried accessing the plc shell, but get auth errors.
Also, when starting/stopping the program via plc shell from codesys IDE it doesnt report that information to log

Beckhoff CX9240 : Using Internal EtherCAT Bus

yannickasselin — Fri, 10 Jul 2026 09:56:35 -0000

Control RTE is for Windows. @arj3090 specified Linux.

Beckhoff CX9240 : Using Internal EtherCAT Bus

eschwellinger — Fri, 10 Jul 2026 02:31:38 -0000

yes, you need to install Control RTE CX.
In that package there is the Internal EthercatMaster / EthercatMasterSoftmotion which you could add then.

Beckhoff CX9240 : Using Internal EtherCAT Bus

arj3090 — Thu, 09 Jul 2026 22:33:55 -0000

Is it possible to get CodeSys working with Beckhoff IO cards connected directly to the CX9240 running Linux?

Recent posts to Talk

Codesys v3.5.22.10 - Internal error:System.AggregateException...Value cannot be null...Parameter name: expLValue

Codesys v3.5.22.10 - Internal error:System.AggregateException...Value cannot be null...Parameter name: expLValue

Beckhoff CX9240 : Using Internal EtherCAT Bus

Beckhoff CX9240 : Using Internal EtherCAT Bus

Dynamic Images

Beckhoff CX9240 : Using Internal EtherCAT Bus

See if application is running

Beckhoff CX9240 : Using Internal EtherCAT Bus

Beckhoff CX9240 : Using Internal EtherCAT Bus

Beckhoff CX9240 : Using Internal EtherCAT Bus