If you are trying to modify the venue version of a piece of autotext and you receive the message "The venue version of this text can not be modified either because the company version is set to override all venue versions or because this autotext entry is set to disallow venue versions", this is because the autotext either cannot have venue versions, or the company version is set to override all venue versions.
If you are an administrator and this is autotext that CAN have venue versions (not all the autotext items CAN - for example, the unlogged in home page text cannot have venue versions because there is no way for the system to determine what the venue should be) then you can change the company version so it does not override the venue versions. To do this, go to the company version of the text (Which is the version that is displayed when you first view the text) and UNCHECK the "Override venue versions" checkbox, then click save. Then you will be able to modify the venue versions.
If you are not an administrator you will have to ask an administrator to open up the autotext to venue versions. They may not be willing to do this as they may want a particular promotion etc to go to all the venues regardless of the venue manager's wishes.