Compilation Error in Process but not in Library: "Expression Activity type 'VisualBasicValue`1' requires compilation in order to run. Please ensure that the workflow has been compiled."

Hi, everyone. I thought I could fix any issue with converting from Legacy to Windows, but I’ve run into one that has me stumped.

I have a library with a workflow that works perfectly when I debug it from inside the library. It compiles and everything.

However, when I use this library as a dependency, it fails. The whole project compiles, making me believe that there are no issues, but then when the process hits that workflow, I get this error:
Get FaxDetails Table: Expression Activity type ‘VisualBasicValue`1’ requires compilation in order to run. Please ensure that the workflow has been compiled.

I narrowed it down to the For Each Row in Data Table activity within the workflow because it will log the number “4” but not “4.5” (had to insert another log and did not want to renumber…)

I authored this post, which has not been helpful for this case.

I think @Yoichi 's post here might be helpful?? But I don’t know how to apply it to my situation…

Here is what I believe to be the problematic code:

Here are some screenshots of: A) the workflow in the library, B) the workflow in the process that uses it, and C) the code:




Thanks for your help! I know we can figure this one out!

can you share with us a screenshot from the properties of the GetFaxDetails Table Activity (the Screenshot B). Thanks

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Sure, here it is:

I decided to ignore the error and see how far I could get, and I got the same error at this “Configure FaxDetails Table” workflow a bit downstream. It uses the same data table that the “Get FaxDetails Table” used. I think there is something the compiler does not like about the data table… But I’m not sure why it would work fine in my library but not here in the process.

Here are screenshots of A) the new error, and B) the properties of the workflow:


can also have other sources as double quote issues. For a massive ghost hunting you can do the following (take backup before). Have all XAMLs close and search with a text editor (e.g. notepad++) over all xamls for all non valid double quotes “...” or „…“ etc …

So at least this issue can be excluded from further inspections

As it is a library we would also recommend to check each Default values defined within

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So, I was able to run the entire process once through because (luckily) the data I need from the table is being extracted before any error is thrown.

The only issues are in these 2 workflows that use the data table, and they are occurring only in the process; not in the library.

This issue is occurring at the exact same type of “For Each Row in Data Table” activity in this workflow that is present in the original one I was having issues with.

Here’s A) the activity in the library, B) the activity within the process, and C) the code that I believe may be problematic??



Does anyone see any characters that might be problematic in there?

I still don’t understand why this will work all the way through in my library but not in my process, though…

I don’t have time to test this today, but could it be the part of the code that says



That just looks suspicious to me, lol. There is no “ColumnNames” field in the “For Each Row in Data Table” activity, but there is a “CurrentIndex” field (ie. rowindex).

Screenshot 2023-01-24 170936


I observed similar one where i used for loop and a ghost for loop has been automatically created by the sequence and it never moved past the error…

Can you try recreating the xaml that you are dacing issue with…try copying the data one by one and do not copy for loop insteqd create a new one

Hope this might help


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Thanks, @Anil_G . This will be my next step. Will keep everyone posted.

2 hours later, and my 2 workflows have been completely rebuilt from scratch. I published them, added them back as dependencies, and… TA-DA, SAME ERROR! Get your popcorn, this one’s not over yet.

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Still working on this issue. I think this may be related to copying and pasting some workflows from a process that I developed in the Legacy framework over to a new process developed in the Windows framework. I was trying to save some time not having to recreate my workflows, but it looks like there are some errors related to namespaces throughout the problematic library and the process itself. Trying to figure out how to take care of these issues since deleting the namespaces with the errors, republishing, and importing into the process did not work.
Example 1:

Example 2:

Hi, everyone.

This issue is most likely due to 1 or more package misalignments. Specifically, the library is using UiPath.System.Activities 22.4.5, but the process that is using that library is on 22.10.3. Furthermore, our Studio is version 22.4. :grimacing:

Still working on confirming that this is the issue, but it is more likely than not the cause.

Word for the wise: keep your versions aligned! :slightly_smiling_face:

Confirmed that having the 22.10.3 version in the process interfered with the library running 22.4.5. Downgraded everything, and it’s working.

Thanks to @ppr and @Anil_G for your help along the way!


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