This is because "1234" is automatically converted to a number and then conversion of a number against an empty string fails.  Here are several workarounds.  1. If you run 3.4.21 or later change the IsEqual line to  IsEqual ("", a, is_empty)  or  2. Use Length() method instead of IsEqual, for example,  Dim non_zero_length, number  Length( a, non_zero_length )  LoopUntil (non_zero_length, END_LOOP2)  or  3. Append some non-digit characters to the test string and then compare it, for example  Concat( a, "x", a)  IsEqual(a, "x", is_empty)  : Support, goodday,  : In the below copied sample the 24x7 scheduler blocks on  : a "Type Mismatch" error although the variable 'a' has been  : declared as a string type. Why ??  : Robbert de GROOT  : Publicis Group - Paris (France)  : DIM is_empty, boolean  : DIM A, string  : set a,"1234"  : IsEqual (a, "", is_empty)  : LoopUntil (is_empty, END_LOOP2)  : // ...  : // ...  : // ...  : // ...  : END_LOOP2:   
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