Warning about non-printing characters

[SILVIASO]

I am running SPSS 26.
The data were read in from a data scanning program and then converted to a previous version of SPSS, maybe 10 years ago.

I want to recode/convert a series of string variables into a numeric variables, but the program refuses to convert some of the strings for some of the cases.  It's not very consistent.

[it also seemed to have read in some text instead of a date for one of the variables, so something just may have gone awry in the reading process.]

So just to see if I could figure out what was wrong, I tried  to run a simple frequencies on the string variables.  I received a warning about non-printing characters.
I've looked that up in the forum, but found the info (from 2006) hard to apply here.
So asking for help in how to find and get rid of these non-printing characters in these select string variables

Here's the output and warning message
Frequencies
Notes
Output Created 21-JUN-2021 12:42:47
Comments
Input Data C:\Users\ssorense\Box\ANALYSES\SPSSwin\@ MADAS Study\@CLEANED DATA\Interview_3_ 7.10.19 processed!.sav
        Active Dataset DataSet2
        File Label #TFx8.0#C:\...\Macular3QuestionnaireAssess.SAV
        Filter <none>
        Weight <none>
        Split File <none>
        N of Rows in Working Data File 158
Missing Value Handling Definition of Missing User-defined missing values are treated as missing.
        Cases Used Statistics are based on all cases with valid data.
Syntax FREQUENCIES VARIABLES ABVIb1date_3 ABVIb1_3 ABVIb2_3  ABVIb3_3 ABVIb4_3 .
Resources Processor Time 00:00:00.00
        Elapsed Time 00:00:00.01


Warnings
One or more values of variable B. Know:Can you give an example, 2 contained a non-printing character. Each such character was replaced by a space. The data file itself was not modified.

One or more values of variable B. Know:Can you give an example, 3 contained a non-printing character. Each such character was replaced by a space. The data file itself was not modified.

One or more values of variable B. Know:Can you give an example, 4 contained a non-printing character. Each such character was replaced by a space. The data file itself was not modified.


I believe the warnings refer to the variables ABVIb2_3  ABVIb3_3 ABVIb4_3 , not the misread date variable.


Thank you for any assistance!