PHP below 4.3.3 compatability.

Hi.
My server runs PHP 4.3.11 and I am getting the following error when user registers with a promo code:
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-warning: preg_match(): Compilation failed: PCRE does not support \L, \l, \N, \P, \p, \U, \u, or \X at offset 3 in /hsphere/local/home/***/freebusinesslist.com.au/sites/all/modules/promotion/promotion.module on line 1031.
-warning: preg_match(): Compilation failed: PCRE does not support \L, \l, \N, \P, \p, \U, \u, or \X at offset 16 in /hsphere/local/home/***/freebusinesslist.com.au/sites/all/modules/promotion/promotion.module on line 1031.
-warning: preg_match(): Compilation failed: PCRE does not support \L, \l, \N, \P, \p, \U, \u, or \X at offset 3 in /hsphere/local/home/***/freebusinesslist.com.au/sites/all/modules/promotion/promotion.module on line 1031.
-Sorry, but the code you have given does not match any current promotion. Please check that it is correct and try again.
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I have used replacement of str_split() function from PEAR PHP Compat package (str_split() was introduced in PHP 5), but the error above - I presume - is related to "offset" parameter which appeared since PHP 4.3.3.

Any ideas of how to make this great module to work under PHP < 4.3.3???