error occured while trying to save data

[mobius]

this error occurred to me again suddenly and unexpectedly;

https://www.lemmingsforums.net/index.php?topic=3332.msg64730#msg64730

It happens when I try to start the program by itself or when play testing. I can't seem to start it at all atm. But unlike explained in that post; it fails to start at all. I can't run NL. Also the attached message appears a little later.
Also: NL keeps running in the backround using up a ton of CPU.

What's very weird is that it was working perfectly fine yesterday I can't recall changing anything intentionally that would cause this. I checked and I haven't moved or altered the bass.dll or the save folder. My save folder is empty however; is this normal? What's supposed to be in there?

I haven't got time atm but I will try the standard procedures before declaring all hope lost.

[namida]

Nepster: I recall experiencing this, and deleting the file with data on level completion / etc fixed it. Didn't investigate exact cause.

[Nepster]

I don't know how to reproduce this bug, so I am not sure how to fix it.

My save folder is empty however; is this normal? What's supposed to be in there?

You can delete the save folder. NeoLemmix does no longer use this folder, because it was replaced by the settings folder.

[mobius]

I found the source of the error: attached my userdata.nxsv. Without this it works.

As stated below; apparently something (which I probably won't be able to remember) which I did or happened in the past few days; which effected this file caused this to happen.

[mobius]

I found this error occurs if you delete levels files within a level pack you were playing (with the player open), close the player then try play testing (with editor) again later (on a level other than the one you deleted).
Removing userdata file works too, but also moving (not deleting entirely is necessary) the entire levelpack in question also works). Also apparently downloading a new NL player and changing nothing else also fixes it.

Should this topic be merged with Simon's?