Here's another....file I/O difficulties.

[stylin]

Code:

DIM Filename,KeyString,RealText,CipherText AS STRING
DIM F,FilePos,I,I2 AS INTEGER

Only CipherText is DIMed as a string. The rest are integers. Change those to,

Code:

DIM as string Filename, KeyString, RealText, CipherText
DIM as integer F, FilePos, I, I2

and you should be fine.

This is another reason why
1. You should avoid multiple declarations (DIMs) on one line.
2. Declare variables only when you immediately need them, ie., not all at once at the top of the program.

Post again if you have any more troubles.