>I agree it seems to be something other than command line length, except that even when there is no syntax error in the concatenated string, it generates a syntax error after exceeding a certain length.

I was suspecting SET MEMOWIDTH was at play here, inserting a soft carriage return and thus screwing the command, but even after changing it to 8192 the problem remains. I even tried to generate the command like this:

replace csrTest.cField1 with 'abc',;
csrTest.cField1 with 'abc',;
...
csrTest.cField1 with 'abc';
 in csrTest

but it also fails after certain length and I cannot see why...

Maybe you should change your strategy and work with an object from scatter name, changing its properties values in the scan loop and then gather name?