Drawing has been saved by a newer version....uh, no it hasn't

[mcoxinterfluve]

I am currently using Civil3D 2018.

I created a drawing in 2018, but now when I try to re-open it, I get a message that says it has been saved in a newer version, and all my objects are proxy objects.  What would be causing this?  How can it be fixed?

[rl_jackson]

Do you have more than one version of C3D on you PC, if so verify that you are using the 2018 version.

[mcoxinterfluve]

Thanks. No, only 1 version installed. 2018.

[user181]

Are you using Civil 3D as Autocad instead of civil 3D?

[mcoxinterfluve]

No. Although I do have Civil3D as AutoCAD installed (I do not really use
it).There is a chance that Civil3D as AutoCAD was accidentally used to open
the drawing at some point. Would this cause a problem?

[user181]

If its the same version it wouldn't cause any problems.

[mcoxinterfluve]

Error fixed. There was a corrupted alignment not recognized. I used erase
all objects identified as "ACAD_PROXY_ENTITY" using qselect, and was able
to open the drawing.