type mismatch error in reclink matching

[Saunok Chakrabarty]

I am trying to match observations based on their text description, from two datasets, using reclink. I have a main dataset, which I have split into a master and using dataset, to be compatible with reclink. This main dataset was formed by merging on a common string ID, and I am using reclink to see if observations merged with the same ID indeed have the same or similar text descriptions (sometimes the same ID can refer to a different observation across the two datasets). I am getting a "type mismatch error, r(109)" when I perform reclink (below).

* Load the "main" dataset
import excel using merge_1927_1928.xlsx, sheet("Matched(3)") firstrow allstring clear
preserve
keep classno concat_new_1927 // forming the master dataset 
rename (concat_new_1927 classno) (concat_new classno_1927) // renaming variables to be compatible with reclink syntax
tempfile matched_set_1927
display "`matched_set_1927'"
save `matched_set_1927'
restore 

keep classno concat_new_1928 // forming the using dataset 
rename (concat_new_1928 classno) (concat_new classno_1928) // renaming variables to be compatible with reclink syntax
tempfile matched_set_1928
display "`matched_set_1928'"
save `matched_set_1928'

* Load the master dataset (ie 1927)
use `matched_set_1927', clear

* Perform record linkage with the using dataset (ie 1928)
reclink concat_new using `matched_set_1928', idmaster(classno_1927) idusing(classno_1928) gen(score)

I am getting this error:
"type mismatch
post: above message corresponds to expression 1, variable classno_1927
r(109); "


Here are dataex examples of each of the datasets (main, master, using):
Main:

* Example generated by -dataex-. For more info, type help dataex
clear
input str8 classno str514 concat_new_1927 str390 concat_new_1928
"01497" "othermeatfrogslegs"      "frogs'legs"    
"01499" "othermeatmeatsfreshnspf" "meatsfreshnspf"
end

Master:

* Example generated by -dataex-. For more info, type help dataex
clear
input str8 classno_1927 str514 concat_new
"01497" "othermeatfrogslegs"     
"01499" "othermeatmeatsfreshnspf"
end

Using:

* Example generated by -dataex-. For more info, type help dataex
clear
input str8 classno_1928 str390 concat_new
"01497" "frogs'legs"    
"01499" "meatsfreshnspf"
end

I thought the error was because the common ID between the two datasets (classno_1927, classno_1928) was string, but that doesn't seem to be the case.