The most common cause for a variable error in versions 1.1 and earlier of Apple III Business Basic is to use SWAP with at least one of the arguments set to a null string: doing so creates an error in the string variable storage area. Unfortunately, these versions of Business Basic don't notice this error until they run short on storage space and try to consolidate all free space; the variable error occurs when the consolidation routine finds the swapped null string. The following fragment of code will generate this error: 10 T$ = "The little red fox jumped over the lazy dog's back ten times." 20 PRINT "Length of T$ is " LEN(T$); TAB(40); "Length of B$ is " LEN(B$) 30 SWAP T$, B$ 40 PRINT "Length of T$ is " LEN(T$); TAB(40); "Length of B$ is " LEN(B$) 50 PRINT FRE This problem has been fixed in versions 1.2 and later.